Jenney was apparently self-taught initially but he later went to school. So does that make him an insider or an outsider? Possibly a little of both? Such discussions are beyond my meager knowledge of the man.
This painting itself has a seemingly haphazard brushwork and a different perspective in any way you choose to define that word. When you see his work you get the impression of what some people might call "whimsy." I would punch those people. He seems to have an actual sense of humor.
There are some hostile critiques of his work out there too. But someone, in addition to me, likes him because he has work in a long list of major museums; Whitney, MOMA, Met and others.