LOL!
We've been in the situation where the teacher will give something way above level and then not explain it. It's the whole slippery slope thing.
It could be a combination of trying to prove you wrong and also not knowing how to handle the situation. This is the crux of the problem with education of HG kids in public school.
You and I will never know for sure. The only think I can say is hang in there. I've come to the conclusion that my kids will never be drop off/pick up kids. There are problems as well as advantages! It won't be hands off, so buckle up and prepare for the ride.
Try to develop good communication with the teacher and just do what you can when you can. Lastly, your child will come home with stuff that just fires you up! Learn to know when it upsets you and when it upsets your child. Choose your battles wisely.

I agree that this situation was not handled well by the teacher. I would also spend some time discussing with your DH privately whether or not there is validity to the teacher trying to make an example out of your child. If you find that both of you agree on that (cooler heads prevail, so try to look at the issue non-emotionally, if possible!) you may want to consider other options............