If it was charged as trespassing, not something higher like burglary, then the level of his trespass was probably the lowest misdemeanor. Usually trespass is a sliding scale starting with a warning not to return.

Being that it was on a campus, they can sometimes use that as an aggravating factor. I remember one case where a homeless person had a key for a vending machine and took out $30 in quarters, but since the land the vending machine was on was owned by a university he was sentenced to 12 years in prison. One of the few cases that got reversed for a constitutionally exceptional sentence.