Parked at a friend's house. Now his stepdad is mad at me. What's the deal?

My friend says it is ok that my car stays at his mom's house in Metairie while we are on a two week trip overseas rather than racking up fees for airport parking. We drop the car off and I let his stepdad know that it is greatly appreciated. Fast forward to they day we return. My friend is at work (It is a Wednesday) and says the keys are in a bush next to the door. I find them and we make our way back to Baton Rouge.

Fast forward again to the weekend and I hear from another friend who rode back with us that my original friend's stepdad is pretty pissed because he saw me walk up, get the keys out the bush, and drive away without knocking and saying thank you. The friend who told me this also said that he shot a few bucks his way to kind of smooth things over if I want to pitch in.

This makes me confused and pissed in my own right.

1) I thanked him before we left even though he stayed sitting in his chair with his laptop open and sort of reciprocated that he heard us. Whatever. I wouldn't care if he wouldn't have ended up acting like this.

2) Why in the hell would I think to knock on the door if I'm getting the keys out of the damn bushes. Because I'm getting them out of the bushes, I assume no one is home.

3) It is mid day on a working Wednesday. Again, I'm not expecting people to be home.

To top it off I have previously welcomed this guy to my tailgate and offered food and drink without asking anything in return. If I knew it was going to be such a hassle, I'd have just parked at the airport.

Am I missing something here, or is this guy just being a douche?