Is video recording on school trip a "privacy violation"?

NOPE.
Everyone who attends a class trip must expect that people will record videos, and that their faces will occasionally appear on those videos.
A school trip occurs rarely, making it special. For all the money and effort put into organizing a school trip, one might want to have the memories on solid watchable video; not just stored on neurons inside brains that will one day get dementia and die.
What is the worst that can happen from video footage with visible faces? Anyone who behaves appropriately can not be humiliated through those videos. And if someone had the idea of sharing those videos online, likelier than not they would get 3 views and be forgotten about.

The same people who cry "privacy violation" at photographers and filmers are the people who in a decade will say "man, I wish video footage from that beautiful day existed".