I had once incident where i was with a fellow SLAPPAL at the UC Berkeley campus - we were cruising around and a campus security came and attempted to kick us out. My friend knowing the rules, in a mature civil manner told her that we can freely roam the campus until midnight, she asked if we're students and my friend also told her that regardless of that the campus rules state anyone is allowed to be on the campus grounds til midnight. She coulda simply told us "please don't skate " rather than approach us with "your skateboarding now I'm kicking you out" ... fuck those kinda ppl who make things more difficult than they need to be
As someone who has been kicked of of UC Berkeley campus many times for skating and has also gotten ticketed there, I can assure you that those are most likely UC Berkeley Police Officers and not security guards (same with BART). They have guns, can arrest you, and, like all cops, can do whatever they want more or less and there isn't much in the moment you can do about it.
I'm shocked they didn't respond well to your friend proclaiming he knew the rules. Cops usually respect stuff like that.
That being said, watch out, SF. All security and cops are going to way overreact to skating for a while.