Haha, how could she have thought that was a good way to handle it...
I donno though, Autistic kids can appear very normal at first and so it makes sense that the kids just thought he was plain obnoxious. Two of my best friends between the age of like 7-10 were autistic and if you only just knew them you'd never know but... the more you got to know them, the more you realized that they had huge issues. I mean they had SEVERE autism too, one would have to take a break every half hour or so to go rock back and forth for awhile, like there were some problems.
The most noticeable side effect of autism is an inability to handle and interact normally in social situations, so that teacher pretty much ruined that kid. Literally the worst thing she could've done given his diagnosis. Even if he ends up not being autistic, having the entire class speak openly about a student and directly call him out so that he realizes his entire class hates him at FIVE YEARS OLD!? Fuck that. Fuck. That. She better get sued, and I HATE lawsuits.