Your friend did what she could in the past. As parents we have more influence over our DC when they're younger, so even if Bob wasn't always keen in the past, he had little choice.
Bearing in mind the kindness she's shown in the past, it's highly plausible that she may have suggested a get together with your DS and her DS showed no interest.
Even if I felt I could force it because I felt sorry for you and your DS, my DH would absolutely not be happy if I was making our DC be friends with someone they'd moved on from....so that's something else to consider.
My Dsis is in your friend's who position. She has a friend who's DD has ASD.
My Dniece doesn't really want the friendship now, but is okay seeing her very occasionally, but Dsis friend pushed her DD onto Dniece a lot during primary school.
She's said DN is a good influence and has a lot of patience with her DD, and her DH (friends DH) has told her to make sure they don't drift apart as they now go to different high schools.
This girl also struggles with friends and it puts my Dniece (same age as your DH) under a lot of pressure. She once asked Dsis if she could tell my DN to play with her DD at school, because nobody else would.
DNs other friends stopped playing with her, because of how the girl behaves and luckily the school picked up on this and called my Dsis in about it. Dsis told them what had happened and they introduced a rota for different children to play with the girl everyday, because it was impacting on DN and because the other girl needed support.
Dsis thought different secondary schools would create a natural drift, but with her friend saying her DD misses Dniece so much my sis has felt obligated to invite her over.
It stresses my Dsis out... then she transfers her stress to me to offload.... because she's too nice or not assertive enough.
The other mum is a very nice lady, but because I'm close to Dsis, I saw how it affected DN during primary school.... which in turn affected Dsis.