What the Fuck Mr. Cop?

So today after school me, with my friends Shon and Lizzie were bored. We decided to drive to this old bridge that was removed from over a river and placed in a field. At the bridge we just chilled and walked around on it, and did some extreme tightrope-like crosses over mud and shit. Not a big deal right? Well we were just playing around and I turn around and see a state trooper. He gets out of his truck and just hand motions, basically telling us to get off and go back to my van. When we walk there he pulls up by the van and asks our ages, im 17, and the driver so he asked to see my licence. He tried to call it in but the lady on the other side said the DMV database was all backed up. Then this tool goes on and tells us how we should all be arrested for destructive behavior on private property, yet there were no signs marking the land or bridge as posted. Anyways he let us leave, I guess something so small was not worth his time. What the fuck was up with all of that? I could understand asking us to leave but why would he threaten to arrest me?