If you're starting from a position where the police can't take any action against you without more evidence, and they need you to provide that evidence, sure. In that case, there may be no benefit to you to cooperating. But that's not where the parent post was.

He was a juvenile, carrying a rucksack, walking alone at 5am. He is already starting from a position of being detained as a potential runaway. His encounter can get better (proving that he's just a birdwatcher and being allowed on his way) or worse (if he's carrying anything he can be arrested for). If he's just carrying a camera and a pair of binoculars, it seems like its worth the risk. The officer has better things to do with his day than ferry around kids who clearly aren't runaways.