@GRex
There's no need for such an aggressive response. The OP's account was pretty clear and hasn't been 'constantly changing'. I don't think she's been sacked either, just asked to leave the room.
OP, unfortunately there are some heads and teachers like this who are on a power trip, frankly. You are a new, inexperienced TA and there are better ways to talk to you about confidentiality and conduct (or what may appear to be questioning his judgement) if this is a concern.
In a new setting, take time to watch, listen and observe how things are done. You may disagree with them and there will be appropriate ways to raise concerns, even low level concerns, during safeguarding training or in the policy. In my training we use a fictional case study of a new, apprentice TA who has concerns about a senior member of staff. We discuss how hard it is for such people to report so you're not alone.
However, be careful about the casual conversations with colleagues that seem straightforward. In a long career in education I have learnt that they can all too easily come back and bite you on the bum.
With regard to the questions, make sure you're listening more than talking, that you've read policy and handbook documents carefully and that you seek advice from the right sources, i.e. your mentor or the really strong and experienced staff. Good luck - TAs are golden and you will make a real difference to children so keep going!