People have a thousand reasons why they do stuff.
This always happens to me when I email someone a question that's important to me and don't get a reply within a few days.
Usually, it's distraction with something totally unrelated.
Give it a few days and see if his demeanor changes. Keep yourself focused on other things.
If after a few days it's the same, and you're still worried that it does have something to do with your boss's feelings about you, you should ask, if only for your own pace of mind.
“Hi [Boss], how are you doing? You seem to be distracted recently. It may have nothing to do with me, but I just wanted to reach out and make sure everything is good between us. Let me know if there's anything I can do to support you with anything these days.”
Dave Wolovsky, MS CAPP
Relationships Coach, answering the internet's questions about all kinds of relationships.