I have only briefly looked at your previous posts re: this situation. I have to say that I think that the problem at this point is the teacher. He sounds young and lacking in knowledge about child development. Your son is only 5 and he does have some health issues. The more attention this teacher pays him the more your son is going to "act out." That's the teacher's word; not mine! I say to that teacher, "cut him some slack! Cut yourself some slack!"
A big clue for me is also his statement about how he didn't act that silly at that age. A big clue! Each and every one of us has to be careful when working with a same sex child that our own unresolved issues at that age aren't allowed to surface and influence the way that we treat that child. It's my guess that this teacher had difficulties with adults over silliness when he was 5. Silliness was disciplined (punished) out of him. He sees silliness as a bad thing instead of the neutral thing that needs to be directed in the classroom into something positive. It sounds like he wants to discipline it out of your son.
I would ask that he change classrooms. I think, that although change could be difficult for your son, I suspect that it will actually be a relief.
The principal may want your son to remain in that classroom and suggest that the teacher work out a way to deal with him. If he does, he's wanting the teacher to learn. Your son doesn't need to be his "guinea pig."
I agree that this person may not be suitable for teaching at this age. Apparently he's started mid-year at a time when it's difficult to find a teaching job. He may not even want to be teaching this age. Emphasis on rules and regulations, except in a broad way, is rare at this age. The fact that he defends himself by asserting this claim is another red flag to me.
I would keep in mind that this is a beginning teacher and go easy on him while quietly and calmly stating that the match is not a good one and requesting that your son be transferred to a different classroom. The principal is aware of this teacher's personality and lack of knowledge and skill. (S)he may consider it his responsibility to work with this teacher to find success. The principal, vice-principal may have not been at the meeting on purpose thus allowing the teacher another experience. By law, the teacher, does have the right to a probationary period during which his superiors are required to provide support. But your son doesn't have to be a part of that plan.
ps If you haven't observed your son and the teacher in the classroom you may want to do that before the meeting with the principal. It's good to have covered all bases. Be cordial to the teacher. Make no critical remarks. Just sit, out of the view of your son, and watch. This way you will be able to respond to particular behaviors. You will, most likely, see some negative behavior from your son. It sounds like a pattern has developed that encourages this behavior. By having seen what is happening in the classroom you can temper your criticism with acknowledgment of the teacher's dilemna; then continue to state that this reinforces the notion that this is not a good match.