So usually when an imaginary friend is a real thing in a story, it’s either a demon or a ghost or some supernatural boogeyman that probably wants to eat the kid they’ve befriended (Mama, a couple of the Paranormal Activity movies), or “imaginary friends” are just treated as a real thing in the setting, and if a child just thinks hard enough they can manifest a friend into existence (Foster’s Home for Imaginary Friends, Happy).
And somewhere in the middle is an area where the imaginary friend in question is real and they are supernatural, but they aren’t malevolent, and they aren’t entirely honest about what they are. Like maybe they’re a fairy or a god or some kind of boggle from mythology, but they just got caught by a six year old and they don’t have time to get into it, so they just go “…Yes. I’m your imaginary friend. We haven’t met. How do you do.” And then they stick around because they do love this kid, and if you’re a boggle from mythology in the modern day good food is really hard to come by.
And at some level. That’s what I think Hobbes is.
He did, in fact, Literally Catch Him. And in the next strip-
Calvin takes him home and feeds him, which is a Humorous Misunderstanding. But also means Calvin is fulfilling: Hospitality Law.