My DS was like this. He has very mild ASD, but honestly, it's hardly anything. I am glad with hindsight that the school raised it, but at first I found it very hard to take, as I'm sure you do OP.
The thing is, that the teachers need to find a way for your son to fit in in class and be able to "access education". If his behaviour is making that difficult, even in a little bit, then they will want to look at why that is. Either they need to discipline him, or teach you to discipline him, or if there is a behavioural problem, then they need to understand what that is.
By flagging up that they see a behavioural difference that is affecting his ability to access education, they are just doing the very best for him that they can. They need to get to a place where they understand what the issue is, so that by the time he reaches secondary school he is well understood, and ready to get the best access to education that he can get.
If you can manage to take it as kindly meant, and to work hand-in-hand with them then that will really help.
One caveat in our case is that the school had very little funding to have the situation looked at by a psychologist. We had to pay privately for an assessment, or else we would have achieved nothing really. If you can pay for a private assessment that will help a lot.
fwiw, I do think that seeming like a highy intelligent twat pain can be a sign of ASD, but it tends to be a specific type of behaviour, that the teachers will be able to distinguish from neurotypical type twattishness. I am diagnosed as having ASD, so I speak from experience. LOL! (Sorry)
Good luck and take care there. I know this can feel very hard.