Have you ever made a mistake in the real world, i.e. not on the Computer, and thought in your head Ctrl+Z? I've done this a few times. I just did it while drawing in my sketch book. I made a line that I didn't want and unconciously said Ctrl+Z in my head. I was like "uhh, okay.."
I think it might be because I also work with Photoshop a lot.