Storm in a teacup.
The doc said 'if' it had been higher, it might have been fatal.
They did not believe the injury was serious enough to warrant x raying.
They said your son was fine to go back to school.
I suspect they refused to discuss it any more with you because they had more serious iPod life threatening injuries to deal with, it being a&e, and all.
The teacher's comment was a bit out of order, but tbh at the time it sounded as though he had tripped over his own feet or walked into the wall, and she was probably trying (in a spectacularly crass way) to lighten the mood. I do the same thing with my kids if they fall (and I have a spectacularly clumsy kid with cp, who regularly gets called a daft head by me if she trips up and hurts herself. Ok for me to do it, but maybe not a teacher)
I think you are blowing this completely out of proportion, and as others have said, you may have been labelled a trouble maker, which is why school are ignoring you.
The only thing school need to do, if you wish to see it, is let you see the accident book. You can discuss the 'comment' if you like, but I think it's yesterday's news, tbh.