It is irrelevant that the kid is autistic. Nobody should ever needlessly humiliate a child or adult in this way.
As John Doyle points out, the superintendent contradicts himself in regard to the reasons this was done. I don’t buy the claim that the play was simply ‘over’. Nobody sprints up to yank away an unused microphone at the very millisecond an event is over, if we could even somehow believe she didn’t see him standing in line.
You also saw that he had lines in the entire play that you watched online. How can a character that does not exist have any lines? And how can the entire play be posted online if there are kids under protective orders?
Let’s suppose the worst case scenario, and that this kid let’s loose a stream of Tourette’s-style obscenities every time he gets in front of a mike. That’s contradicted by your claim that he’d already delivered other lines without incident, but let’s go with it anyway. Is this the best way to handle it? Yanking the mike from his face in front of everyone? How about cutting the receiver off? Or just getting the kid off the stage?