PS, voting me down won't make the article any more on-topic, and it doesn't matter anyway, I have oodles of this karma shit, and if I have to burn it pointing out the reddit-bait, so be it.
In full consideration, genuine question, would you rather cops simply drove by when witnessing people with damaged public property in hand or would you rather they stopped and made some sort of enquiry?
Did they arrest you, what crime did they claim they were arresting you for? How did you avoid being arrested if they said that is what they were doing? Either they arrested you or didn't, if they didn't they were making an enquiry.
Yes, perhaps they hedged their bets and thought that you might be scared off damaging public property if you had perpetrated the offence by the apparent threat of arrest.