The teacher is basically saying he doesn't want to learn, doesn't want help, and there's nothing she can do for him if he won't make any effort at all.

I get it. It's hard to motivate kids. I drove mine through the worst neighborhood in our town (really third-world conditions, sex offenders on each block and yes, i showed them the map) and told them that if they don't want to live in those conditions as adults, they need to try harder.

Your SS may not be an academic but he should be told he had better damn well have some kind of a plan for when he's an adult if he doesn't want to do school. Pretty much every post HS training program requires at least a diploma or GED, too. 

The teacher sounds frustrated and like she's run out of ways to motivate SS to do his work.  There's not a whole lot a teacher can do with a kid who doesn't do any work and says he doesn't care if he fails.  She's probably looking for your DH to light a fire under his kid.

Not every school does detention.  Basically that's asking the school to punish/babysit the kids when the parents should be responsible for disciplining them.  My school had a "homework detention" for kids who were failing/needed extra help, but if a student wasn't willing to do any work while there, it made no sense for teachers/paras to waste their time watching that student do nothing after school.  Those kids were usually a distraction to others, too.

Your DH needs to figure out a way to motivate his own child.  That's the teacher's job only to a point.  The teacher can only do so much.  Your DH can take away electronics, ground SS, give him extra chores, etc.  He can also "bribe" SS and provide rewards/positive reinforcement.  The teacher can't do much of that, and also doesn't know SS's currency the way DH should.  Suggestions to the teacher might include asking her to let DH know when SS misses an assignment so he can give an appropriate consequence at home, or letting her know if SS has a particular currency she could use, or if there's some different approach that works with SS that she might try.  But the bottom line is that this is your DH's problem, and maybe the teacher is gently pointing that out.

Your SS14 sounds just like my SS14. And the teacher sounds like me lol. I wish SS' teacher would even let us know when he doesn't turn in his homework. 
it is nearly impossible to motivate a person who just doesn't want to do the work. 
If we want to make sure ss does what he's supposed to do, the only way is to be on his arse and ask every 10 minutes to ensure the task is done.

it is insane and I'm at a point ready to let him fail. 

Detention is usually for breaking rules, not refusing to do homework. She's looking for ideas to motivate him. 
 

My SS21 was like this, although he and BM lied better about his failure to do work. 
 

Prepare for failure to launch, just make sure it's not at your house. 

Keep in mind that this teacher probably sees 150 students rotate in and out of her classroom daily. Assuming 5 periods w/ 30 kids in each classroom. She cannot hand hold and force one student to do the work he refuses to do. She has pretty much told the parents that she can do no more and they need to step it up or accept their child failing school. 

Is this a pattern w/ this kiddo? He won't do what he doesn't want to do and no one will change that?

That teacher is saying, without saying: This kid is an A-hole who is defiant and nothing I can do or say will change that. I have no real power. You are the parents and need to figure it the F*** out. I don't get paid enough for this crap. Don't use me as a punishment if you have no follow through at home. You are wasting my time. 

I agree with her. Something has to happen at home that makes an impact. If that means no electronics, no friends, extra yard work or housecleaning-- whatever it is, make it AFFECT him. It has to make a BIG IMPACT or nothing will change. SS21 (autistic) is the worst with this. He will say whatever he thinks I want to hear. He will do something for a day or 2, make a huge production of it and then stop/start right back to his old ways. It is so frustrating and unless I do something crazy and drastic nothing ever changes. I have to go full psycho mom yelling and making his life miserable! It is draining to me, but the only way to make a change. Your DH needs to step up BIG TIME. 

The teacher is saying that he is a waste of flesh and they  are done wasting time on the kid and putting punishment on the parents where it belongs.

The teacher is right IMHO I would boot this kid's ass out of my class and let him fail if I was the teacher.

 If I was the parent it would be game on with a daily paddle to the ass for non performance followed by hours of shoveling yards of gravel into buckets and moving the pile back and forth across the yard for weeks on end until that kid would be crying and begging to do homework.

The teacher is simply covering their bases.  When/if this gets brought up to the school board, or the principle, the teacher will be able to show where they contacted the parents, tried all the normal school approved disciplinary actions and still had zero results.  The teacher knows the kid won't do the work, and that nothing will motivate them.  This is their way of CYAing so when the parents whine and complain their special little poopsie is failing and they had no clue, or the teacher didn't try to work with the kid. the teacher is covered.  I really feel bad for the teacher, they have better things to do with their time than cater to these a$$hole kids and their a$$hole parents.

I think everyone else has covered the "what did the teacher mean?" question. On how your DH should respond, that's a bit trickier.

How he SHOULD respond is by stepping way up as a parent and holding his son accountable. Same goes with BM. He should outline to the teacher exactly what he'll be doing to hold SS accountable, and then give the teacher free reign to contact him should SS ever be a pill to her.

But, if your DH won't do that (and it sounds like he won't), then he needs to tell the teacher to stop trying to help SS, give him detention if he's disruptive, and accept that SS will fail and have to retake the class. Perhaps your DH should recommend a lower-level social studies class, or summer school.

If your DH isn't going to step up and be a parent, then he needs to be upfront with the teacher that he's fine with SS failing and she should just stop trying with him. It should be embarrassing for your DH to say, but better for him to tell the truth than to either expect the teacher to try harder than he does OR lie to the teacher where she still tries to give a damn.

Without accountabillity you have Kaos lol.

There is no ME in Family.

Everybody has a job and to function we all have to do our part.

Good luck regards Jake