Good on you for reading the guy the riot act. Sadly, he is most likely one of these folks who thinks he is never the asshole, everyone else is.
In Scouts, at the end of every campout, we would form a police line and police the site - everything came up, regardless of whether it was left by us or not. AT first, the adult leaders would assign pushups to the whole troop for every missed item we found. As the boys - and the Troop - matured into a boy-led troop, the boy leaders would designate the pushups for missed stuff.
It worked well, every camp site was cleaner when we left than when we arrived.