I agree that it's a heartwarming story that people wanted to support the boy, but agree with Celia. This story has been irritating me all week with the parent bashing.
Just because you are invited to a party doesn't mean you have to attend. I admit to pretty much ignoring the "whole class" invitations and sticking to the ones where I knew the parents or my child was particularly fond of the birthday child. If my child had never played with the child outside of school, they didn't go.
If an invitation was addressed to my child by name and had RSVP information, we did so. If my child had an invitation without his name on it that he was just randomly handed, we ignored it. Many times they said things like "a kid handed me this on the bus."
IMO, birthday celebrations should be with people who know the child well and love him/her. If that means family, fine. If that means just neighborhood kids, fine. If that means a few people from church or a social group, fine. If that means special friends from school, scouts, or daycare, fine. But I simply don't get the "invite the class" thing.
I don't think this really was about the boy's autism spectrum diagnosis. It happens to anyone who does the generic whole class invite.