Is Calvin an unreliable narrator?

Per Bill Watterson

Calvin sees Hobbes one way, and everyone else sees Hobbes another way. I show two versions of reality, and each makes complete sense to the participant who sees it.

He is reliably telling what he experiences, and the reader is not given enough knowledge to tell whether he's deluding himself or experiencing something that others can't see. (Though we do notice that Calvin's father saw him tied to the chair, which Calvin could not have done to himself, which is at least some evidence toward Hobbes being real.)