What makes you think they are trying to kick him out?
I doubt a state school would ask your son to leave if he is autistic. It's discrimination for a start.
Autism isn't the end of the world, and it is not something that can be detected by having s speech pathologist observe him one time.
You have the option to play into their hands, have him assessed properly.
My friend has fought her daughter's school for help with behaviour that she was convinced was due to special needs, all the teachers (bar one) and leadership staff refuse to see it! So far one of the three of her children has recently been diagnosed and the other two are sure to follow with a positive diagnosis. '
If your school has concerns bout your dh, you would be daft, in my opinion, to NOT follow that up!
If he is, then they can help him and you can too
If he isn't, nothing lost, but you ask the teacher where to go from here