How do you know Crazy?

I was subbing in a special ed classroom, and I was warned about a boy I was to be working one-on-one with. "He's crazy. Like actually crazy. He just says random things. He hears voices."

Going with this information, I was not phased when he would stop me and say "hold on a sec--" and then make some strained facial motions whilst moaning some almost-sensical phrases. He would then conclude this by saying "Sorry, that was from [name of a movie I know exists but have not seen]."

This was the most crazy thing he did to me, in the several days I worked with him. I wonder if this is really evidence of a reaction or response to voices in his head, or if this is an attention-seeking / ADD / Autism Spectrum thing. I know that higher functioning kids on the autism spectrum will sometimes memorize lines from movies and employ them when it seems fitting, as a way of trying to be part of common conversation.

Perhaps they've taught me about too much for my own good, and all my special-needs education forces me to diagnose every quirky kid I meet. Or perhaps I'm right.