I suspect that this year's teacher probably didn't know about or didn't remember that this child had bullied your ds last year.
I'm not a teacher but I'm guessing that while you may be aware of friendship groups within your class/year, you probably don't always remember the history of every child's interaction with other children, particularly things that you weren't a part of actively being involved in (like the teacher from last year). Even if you were told about it, you might not necessarily remember.
If you are busy and stressed, and you have some parents come in concerned that their child doesn't have any friends, but that the child has mentioned that xx and yy are nice kids, then you'll probably think 'poor kid, I'll get xx and yy to play with him at break time and see if they will give him a chance to be friends'.
What are the chances that the parents told the teacher that the reason xx doesn't play with their son is because last year he bullied him? Pretty minimal I'm sure (were the school involved with sorting out the bullying at all or was it just you telling your ds to stay away from the bully?). So the teacher would have just had a one-sided conversation with the parents and thought he would do something about it as the parents had asked him to.
I'm not trying to condone the teacher's actions, I'm just saying that I can understand that he got caught up in the moment of trying to help a child after his parents had been to see him.
However...
He certainly shouldn't have asked your ds to play with him exclusively - he could have asked him if he and his friends would have minded playing with him for one break just to see how it went.
He certainly should have given your ds a chance to say no if he didn't want to - with or without an explanation.
And once you talk to the teacher, he should certainly say that he won't ever ask your son to do this again, regardless of what the other child's parents request. You need to decide before you speak to him whether or not you want your conversation with the teacher to be relayed back to the bully's parents - ie do you want the teacher to tell them that he has spoken to you and as a result of your child being bullied by their child last year, you have requested that your son is actively kept apart from their son. Or do you want the teacher to gloss over why he is not forcing your son to play with their son?
Also sounds like a good time to bring up how the school deals with bullies in general (it's not good that your son felt he had to play with someone who bullied him and didn't know how/who to talk to someone in order to get out of this without feeling that the teacher would be angry with him) and also how they deal with people who don't have people to play with at play time (things like benches where people who want to play with someone can go and where kids in the top year take it in turns to be play buddy monitors etc) can all help.
Do you think that their son is socially awkward, has always liked/wanted to play with your son and his efforts to become friends with your son ended up with your son being bullied (maybe because he has no good role models at home, or isn't good at doing the friend thing, or gets jealous and wants a friend all to himself or whatever) - which is why this time he has requested that he wants to play with your son rather than any other kid in particular? Or is there some other reason that he might have picked your son (smaller so easily pushed around, very popular so he wants some of that popularity for himself, etc)
Sorry lots of questions and being devil's advocate, not so many answers.
Hope you manage to get it all sorted for your ds on Monday, sounds like you will be able to speak to the teacher and hopefully it won't spoil your weekend...