Personally, I don’t think J’s music theory really goes that deep. In his songwriting, especially the early stuff, it really seems like he’s just playing what sounds good rather than anything from a technical standpoint. He’s a very erratic player.
I’m very similar (though obviously not as good), and despite playing for many years and having some degree of musical theory, I can’t really assess the key of songs or what have you. I don’t believe J does, either.