How interesting, my 15 year old is Autistic and my 3 year old isn't, my breath has been utterly taken away by some of the attitudes on here.
Savantism (the "cleverness") in Autism is very rare, though the examples are normally amazing, the ability to draw from memory etc (there's quite a chance Mozart and Einstien were mildly autistic).
Autistics live in a constant state of high anxiety, loud noises terrify them, my son runs off if a road drill goes off or a fire alarm sounds, police sirens made him sob until recently, I doubt strongly the Autistic acted with any malice, possibly the child screamed or shrieked and it was a terrified fight or flight response, I can see why he was taken to a Cafe too, somewhere usually quiet where he could practice normality.
My son has enough going on to realise the social unacceptability of this sort of action but some haven't.
About ten years ago my son shouted, something incomprehensible, really loudly at (or near anyway) a child in asda's and the kiddie, understandably started crying, the mum got the dad, despite my apologies and explanations who asked where I got off bringing "maniacs I couldn't control out in public" and "I'd put him in an effin cage".
I left my shopping there and took my son and wife back to the car, as we were going out in the car he was coming out of the doors and he stood there half in the road staring at us aggressively and nodding his head.
I got out and fractured his skull and eye socket, got a fine, community service and 3 years probation but the judge had a few choice words for his attitude too.