Uh, you'd be surprised how serious "words on paper" can be.
OP didn't provide any details about said paper and only decided to say it told "about him and his friends".
So i'm going to go out on a gigantic limb here and guess it was just notifying everyone that stupid kids are walking around and forcing the gate open.
It's not like he got a letter that had a gigantic fine, said that he was getting sued, or any other extent or definition of "trouble" you or I can think of. If this is the case, however, it's his fault for leaving out such mammoth details.
The "words on paper" are of no value to be worrying about unless they actually decided to follow up with punishment.