Trust your instincts @Chilli89
My DD had a teacher I wasn't sure of, found her ignorant and vacant. She was dismissive of my concerns for DD.
I left it, thought the same as you that she was probably stressed with a new class.
By Christmas my DD was being so badly bullied and she did nothing whatsoever. I had to hear about the serious nature of this violent bullying from a parent, and assumed she didn't know. But when I raised it she did indeed know and felt DD needed to be taught resilience instead of dealing with the bully.
In the January I asked for DD to move class but school refused. That whole school year was wasted as DD became a school refuser, and learned nothing because she was so anxious and upset.
We moved the school in the end.
Be polite, ask about the shouting incident and don't tell her at first you witnessed it, say your DS mentioned it and let her explain. If she lies, and you know she is lying, go to the headteacher.
She should be aware that your DS doesn't have a reading book. If he's a quiet, well behaved lad he could end up falling through the gaps of the ones who get all the attention. Not giving him a book and ignoring the fact from you is plain rude. Make notes of any behaviour which singles your DS out by her.