Am I the a**hole for taking my friends private keys?

TL;DR; I had a friend over who wanted to play a game of Minecraft together. He was playing a new world he had just created, and I had a look on his PC for him. I found a wallet and private key, which I took and went home with. I put it on a USB drive and put it on my desk. Now he thinks I’m a scumbag, but I think he was trying to trick me into stealing it. Is he right?