Is this considered tresping?

My friends and I went to a public high school to skateboard in Fremont, California (Mission San Jose High School). My friends and I hopped no fences in order to enter the high school, we were able to get in because the school is open. We skated for a little bit and the principal asked us to not skateboard. We stopped skating and we left the school. After we left, my friends and I got thirsty so we went back to the school just to use the water fountain (we held our skateboards the whole time). When we were done drinking out of the fountain we sat down and set our boards aside. Then somebody came in and said he had no patience and said next time he sees us he will call the cops and try to get us arrested (we're only 13). All we were doing was sitting too. We were really tired and our parents were going to pick us up, so at the exit of the school there was a stair set that we just sat down on waiting for our parents (we didn't skating here at all also). This place was only 10 feet away from the street, it was completely visible too. As we waited for our parents to come, the same man who didn't let us sit previously after drinking water got in his car. He took out his phone and started to call the school police. We kindly told the man that we were waiting for his parents. He simply said that he didn't care. I told him we were just kids, and then he was like give me some identification of yours, give me your cell phone. He was being really rude and harsh. My friends and I made a run for it and then he found us eventually in a deep residential area. He then took my friend's phone and called his mom and told her how we can go to jail and everything. He told her everything but the fact that we were just sitting down. If you were to go inside the school, you can see people walking their dogs or just hanging out. Does what we did count as tresping?