Well I wasn't there, and we can only speculate at what was going on with parking.
BUT, if it looked like there was no way to contact owner, no PA at event, and it looked like you were going to be there for a while, and they had definitely parked wrong. I'd probably do same. Though I'd make a fair effort to contact owner first. (maybe smash the window and look through glovebox for anything that could reveal the owner?)
Its grass, it didn't hit anything. Honestly what are cops going to do, you haven't damaged anything.
But lets go back to speculating the guy yanking it is completely in the wrong, because his mate has a mullet and they put it on FB. Its more fun that way.