Perhaps the teacher didn't bring it up. You can't control what kids are taught in their own homes - one of the kids could have said "jews hate muslims" and the teacher may have responded even with something like "in some parts of the world it is sad that there have been fights because of jews hating muslims or muslims hating jews but that is not the way it should be - we are all equal" KWIM.
I really find it hard to comprehend that kids that age would be speaking about world politics to one another in the playground.

He specifically said that his teacher said that to him and the class.

DS came home from school today and i grilled him. I asked if he was pulled up by any teacher asking him about the complaint i had made today. The school's psych had asked him if he believed what he had heard from the teacher, that the jews hate the muslims and vice versa and DS replied that no he didn't it. No he didn't because mummy explained to him that there are the good and bad in all races and religions and not to stereotype. He was also asked which teacher told the class this.

i haven't heard from the school as yet, but i will call in the morning.

My DH tells me to get over it and that i was taking it overboard