Hi hopesav, welcome
I think anything can be a trigger. But male friends among themselves do act differently - its a macho thing. There isn't harm in acting differently among his mates, its a strange humour thing and its enjoyable for men. Don't worry about that.
As for his bad bullying memories they will take time to fully heal. Not much point in making a topic out of it now unless he is in a good environment like camping and the truth comes out and he tells them the effect of it. But these "bullies" were younger then and not fully responsible for their actions.
Best for him to accept that these old friends are different than they were.
It's highly likely they feel much guilt about their behavior but like your man they don't feel comfortable mentioning it.
Triggers, mostly they remain with us for life.
Tony WK