Maybe, but I would definitely have him evaluated by a developmental pediatrician, pediatric neurologist, or child psychiatrist just to be sure. The school has a financial incentive to avoid giving a diagnosis of ASD so I would go with an independent eval.

Selective mutism is one disorder related to anxiety http://en.wikipedia.org/wiki/Selective_mutism. There is something clearly not right but impossible to say whether autism or not. I have heard of at least on ASD child that become selectively mute for weeks which freaked out the parent a lot.

Personally, I do know of a 3 year old who becomes mostly mute with strangers and at school but can speak perfectly well with his parents. I was able to get him to open up and talk / interact with me in my home after a while but he didn't speak to any other kid at our house. His mother was obviously concerned as well but to me, he seemed a lot more NT than our HFA ASD son at that age.

I would try to have a play-date at home with one or two kids from school and see whether he opens up at home with these kids.

My child knew all that in English and Spanish by the time she was 2 and was still diagnosed as being autistic. Autistic kids tend to learn quickly because they can focus better. A language delay though, doesn't necessarily mean autism though. Research to see if he has other symptoms relating to autism and maybe have him tested by a specialized pediatrician because my regular pediatrician missed it.

Your child could be autistic but the only way to find out is to have him tested. If the school has tested him and you suspect they missed something you can request they retest, however I would suggest getting him tested by an outside entity. If you suspect autism a neurologist would be a good place to start. Hopefully your insurance will cover the testing but if they don't and you can't afford it you can request that the school pay for it. They will only do this if they do not have someone qualified on staff such as a school Psychiatrist, otherwise they need to provide psyche testing.

Thanks everyone for responding so quickly. Means a lot to me. Will surely have him tested as well as change his diet and keep you guys updated on his progress. Thanks again