[senco-forum] How to respond to apparently autistic adults

I would appreciate the comments of those on the forum with experience of working autistic adults.
At a recent classical concert I went to, the youg man behind me started to hum along loudly, during one of the quietest parts of the violin solo. This is not usual behaviour at classical music concerts, where even a slight rustle can bring glares from those around you!
I had already noticed this young man during the interval as his behaviour was slightly "different" and wondered if he was autistic. 
I was unsure how to respond to his humming. Which to be honest, I found absolutely ruined that part of the concert for me. Is the problem my lack of tolerance - should everyone be free to enjoy the concert in their own way? 
Or should I make allowances in case he's disabled by autism and not able to understand or see the need to conform? 
Perhaps I should have clearly and firmly signalled to him to be quiet - was it unfair to expect him to pick up the subtle social signals of glances and frowns from those around him?
Or then again maybe I should complain the concerts organisers for allowing him in to the concert at all...
Obviously I am trying to open up debate here; but I genuinly wasnt sure what response would be most helpful to him.
Kate