I know you were EVIL!

Hence, as long as Ace pick-pocketed a storage ring with Qi Mark, it counted as a thievery score! 

Ace also found out about it when recently when he first raided a hidden place. He first thought that he won't even get one count because the ring was just laying in a place, not on someone. 

However, when he used pick-pocket, something happened completely out of his expectation and he got all the storage rings with Qi marks counted, and those people even received thief symbol!

This make things easier for him and at once he was collecting more thieveries with no real danger. 

As for why those people did not give one person their storage rings and have him hide them, so no other person would know. It's very simple actually, they don't trust each other.