K.B.
I agree with everyone else's suggestion that the teacher is not qualified and probably should not have suggested autism, however as a mother of a child with Asperger's I'll add this....
You say he was evaluated twice and the results were negative, by whom was he evaluated? Asperger's is especially hard to diagnose at a young age because they are typically more advanced in language skills as opposed to children with more severe autism. If he was evaluated by a psychologist or developmental pediatrician I would accept the diagnosis but if it was the school district doing the evaluation I would go to a professional. My son was evaluated by the school first and we were told there was nothing to be concerned about and 6 months later a developmental pediatrician diagnosed his Asperger's.
Yes, some of the things you mentioned can be some of the signs of autism, but each one on it's own can also just be part of a typical child's personality. Autism is a whole package of things, not just a few tendencies here or there.
If you have not seen a psychologist who specializes in autism or a developmental pediatrician, I would start there. If you have seen one of them (and you felt comfortable with their evaluation) I would simply tell the teacher that you've already gone that route, and you have been told that everything is fine.
Good luck,
K.