You keep ignoring the FACT that he was leaving when prevented to do so by being assaulted by a cop. If you were leaving someplace and were prevented from leaving by a cop would you be trespassing?
I don't think you have your facts straight. The CSOs tried to ID him, and he refused, so the PD was called.
This is all a setup for a lawsuit.
You keep ignoring the fact that he refused to comply with the CSO before the UCPD arrived.
If I refused to leave at the library CSO request, then yes, I am tresspassing and would not be surprised if law enforcement then detained me to determine my status on campus. Could I be on drugs, suffering a schizophenic break (not uncommon on campuses since most suffer their first break between 15 and 25) or just an every day theif/pickpocket laptop lifter?
This kid's attitude drove events. What his motivation was is now open to investigation.