I'm not sure where anyone's got the idea that I'm trying to force anyone to play with my ds. This has never happened. My friend and I catch up weekly and our children are with us, that is all. My ds will happily play on his own. My concern was that when he extends his friendship to this boy he gets blanked. I don't want my ds to stop being friendly to other children because of the response he gets from this lad.
If the other mum is trying to deal with it, that's all she can do. She can't force the boy to play with yours.
Quite. And nor would I expect her too.
What I did insist on was manners- he had to say hello, goodbye, and answer questions.
This is actually all I would like to see. My ds gets blanked when he calls this boy's name in the playground, or says goodbye to him as we're about to leave. When prompted by his mum he simply says he can't hear him.
Why don't YOU make friends with the other little boy instead of asking your son to do so?
I do have a good relationship with him, he seems to respond better to adults. And I DON'T ask my ds to try and make friends with him, he does this naturally. Going back to manners though, he won't say hello or goodbye to me either.
So why don't the two of you take a simple game along and get all four of you to play it together so the other boy isn't being forced to interact but is still 'playing'.
I'm afraid he sits out of these games too.
imagine you were the parent of a little boy who liked to play quietly, not be forced to hug on demand etc, and someone else was constantly trying to trample over his boundaries?
This is not what is happening at all! I really don't know where you got that idea. My friend is herself trying to encourage her son to respond to mine 
I think maybe just reminding your DS, when they are together, things like everyone is different, X wants to play quietly, why don't you play beside him/play with mummy etc would help.
This is what happens anyway. It is the politeness that is missing, I honestly don't care if they don't play together, I just want my ds to be acknowledged (or to know that being ignored won't affect him negatively, which was the whole point of my OP).
If we spend a very long time together, longer than 3 hours, he will indulge in a game of chase or something with my ds, and they have a wonderful time together. Usually as we're about to leave though! It's not constant hostility from him or anything like that, my only concern is the lack of response my son gets from his approaches (which are by no means boisterous or in your face, merely polite).