You are touch sensitive, startle easy, or simply a jumpy person. It doesn't necessarily "mean" anything, just like some people are really ticklish where most aren't. I happen to be that way, I startle real easy and that's because that's just the way I am.
You just have an exaggerated startle reflex. Mine is so bad that I once had a boyfriend who took to announcing from the living room that he was about to come into the kitchen so I didn't jump sky high when he walked in.