It probably looked like Steve. The story repeatedly hints at his friend steve being killed or taken by the things in the woods.

I don't know about you, but many people would hesitate to shoot something that looks like their best friend in the head.

Or maybe he just panicked because it was rushing him.

Grab a knife from the kitchen and book it out the door. Find someone you can stay with, tell them, then call the cops when the doors are locked.