If he's looking in the window then he's interested in you. Growling is just because he's nervous....maybe indecisive because he wants to be your friend, be warm, fed and secure again but has had bad experiences. I don't think he is wild, just a stray or wanderer.
When I found opossum in my coop this Fall (walked through the open run door, he was eating chicken food) I never had seen one around before but I know we had them because of the roadkill here...along with foxes, raccoons and hawk and owls. Sometime you never see a trace of them, they are very good at avoiding humans. You need to Ft. Knox your coop.
Sophie is cute.
I did the collar with a note on that black stray that showed up and after a few weeks I decided she was free to rehome. One of the nicest cats once she got over her traumatic stray experiences.
A cat sniffing around the coop can mean a lot of things. Cats investigate their environment by their sense of smell. Think of everything else that might be walking around the coop stinking up the place. A cat might also be looking for mice or voles. You have chicken feed, you probably have a field mouse or two around. I think many people lose a chicken, see a stray cat that shows up because it smells a fresh kill and think they have the offending party. It's an easy mistake to make when you are in shock over losing one of your flock to a killer. I guess I'm just not a 'kill them all, let God sort them out' kind of gal and I won't punish an innocent animal for the crimes of another.
I'm not saying cats can't and won't kill chickens, I'm just saying make sure you take aim at the true source of your loses. And secure that coop!