The objection was not to handicapped people being at the show, it was to behavior. It doesn't matter who it comes from, constant loud noises are disruptive and annoy performers and other audience members. It would have been better if he'd taken an early break and spoken privately to the social worker. I think he was justified in deciding not to play if he couldn't concentrate.
I've been part of an audience and band at events attended by handicapped people and never noticed a problem. Folks with Tourette's can't help it, and I don't have a clue what I would do if a one or more of them were making noises. As an audience member, I think I'd be more able to ignore interference and not get mad because I'd know they were not being rude. But a performer has got the right to decide if he can perform under unexpected adverse conditions.