The player's valuables are kept there. They leave their wallets, their phones, their jewelry and anything else they normally carry with them. They put them into bags and leave them in the tent.
This little hoodlum shows up with a back pack. Who walks around with a back pack nowadays?
I suppose you could take stuff out of the player's bags, and the back pack would make it easy to carry anything you stole.
That is a good rational answer (though how stupid would Karmelo have to be to think he’d get away with it? Strike that question — I’ve seen his picture...).
Concern over theft also potentially explains why Metcalf wanted the intruder out of the tent.