In Willa Cather's "Paul's Case", the author specifies how the story of Paul is a "study in temperament". This basically means that it is not Paul's life that is under scrutiny, but the behaviors that lead him to live life the way that he does. For this reason, it would be inaccurate to think of Paul as not human. Paul's odd behavior and his incapability of accepting his reality are a result of a nature that is actually hungry for life, albeit, only what is aesthetically charming about it.
To categorize Paul as not human would reduce his uniqueness in a very negative way. This is because, perhaps, Paul is actually too human. The emotional nature of his character is more accentuated than the average individual, because the average individual becomes hardened and coarse with daily life. Contrastingly, Paul nurses within him a huge passion for things that are beautiful, unique, and exquisite precisely because he understands the human talent for aesthetics and puts it on a pedestal.
Unfortunately, Paul is not within his element. He has a very weak disposition, a passion for sophistication that touches on exaggeration, and a constant self-absorption that indicates a person who seems to be in an eternal state of meditation. In Paul's case this "meditation" comes in the form of fantasies and daydreaming. In it, he sees the beauty that he wishes to have around him manifest, and it is the only motivation that he really finds around him.
We could counter-argue that Paul's extreme behavior does not fit the typical individual. We could even propose that, perhaps, Willa Cather intends to portray an ethereal entity that has somehow lost its way in the world. After all, even his physical description does not match his spirit:
Paul was tall for his age and very thin, with high, cramped shoulders and a narrow chest. His eyes were remarkable for a certain hysterical brilliancy, and he continually used them in a conscious, theatrical sort of way, peculiarly offensive in a boy. The pupils were abnormally large, as though he were addicted to belladonna, but there was a glassy glitter about them which that drug does not produce.
However, this would again reduce Paul's character because there is much about his life that is, actually, quite normal. The problem with this "normalcy" is that it is boring,unchallenged, and unattractive. The boredom in Paul's life, however, reinstates the fact that he is quite human, just one who is not mentally nor physically equipped to accept and tolerate his circumstances.
Willa Cather gives a small explanation at the beginning of the story that may help the "average person" understand someone as unique as Paul.
Perhaps it was because, in Paul's world, the natural nearly always wore the guise of ugliness, that a certain element of artificiality seemed to him necessary in beauty. Perhaps it was because his experience of life elsewhere was so full of Sabbath-school picnics, petty economies, wholesome advice as to how to succeed in life, and the inescapable odours of cooking, that he found this existence so alluring, these smartly-clad men and women so attractive, that he was so moved by these starry apple orchards that bloomed perennially under the lime-light.
Yet, with these facts, Cather does not try to make the reader accept Paul. She merely exposes his character in order for the reader to, somehow, learn to understand his unique nature: A nature which is different, odd, and eccentric, but, nevertheless, quite human.