We all woulda coulda shoulda done something differently. The fact is, no one wants to think the worst will happen. I think it's a good thing you were thinking smartly and like you said, he could have had a gun so in retrospek a little scratch is nothing compared to being shot in the face.
Keying is no fun, though. I know this first hand. Mine are too long and deep for Scratch X to do anything about but I do it everynowandthen to get some of the dirt out that builds up in there.
I knew someone once... I won't name names!... that had a parking spot stolen at the mall during Xmas. This person yelled at the man who stole his spot and the man just laughed and walked away. He had a rather fancy brand new SUV so this person found a spot, went over to the guy's car and keyed "F YOU," but writen out in his door. I know that's not the answer to anything but boy I bet that guy never stole another spot again.
