Being a maintainer of several open source projects myself, I'm well aware of that. I'm not trying to tell him how to run his projects, I'm merely explaining why I did what I did. But I find it rather condescending and disrespectful asking me to jump through hoops to get my changes accepted. It would have been just as much work for him to click "Merge" instead of "Close" now.
For future pull requests I would have been happy to respect his workflow preference.