Hit And Run?

So I just got home from school, college, and it turns out I swiped something at the right end of the back bumper. I've been trying to think if I could have hit anything, but I honestly can't think of anything that I wouldn't feel that would hit the paint so hard you see a big spot completely without paint and not feel it. My only possible explanation was between the 10-15 mins my car was actually parked someone could have hit me or I accidentally hit this one other car.

See, this car was trying to get into a spot, he saw me behind him so instead of backing up to straighten himself out he stopped for awhile, so i passed him. If, by chance, he backed up or I turned my car too soon, would that be considered a hit and run since neither of us noticed?

If so then if he backed up into me by the time my car was that far ahead of him would it be my fault or his?
Synthio Synthio
18-21
Sep 10, 2012