I would not have made an issue out of this. I would consider the action a judgement that is slightly offensive to some, and innocuous to others.
Is the objection that it bruises our frail sensitivities? or that some leftist wants all memory of the brutal muzzy attack on humans thrown into the dustbin of history?
Guess you didn’t know anyone who died on 9/11. I did, a colleague who was on Flight 95. The teacher lacks maturity and common sense. Not unusual these days.