Can you help me understand why people are being hostile to my claim that I have orders of magnitude more subject matter knowledge than they do? The most obvious explanation is ugly – that it makes them feel inferior by comparison, independently of whether or not I have any smugness about it (which I don't).

Well, let me tell you: academics often come across as somewhat smug to everyone who's not an academic.

But, you missed an even more abundantly obvious explanation: you're an outsider, so anything you say, other than blatant gestures of joining-the-ingroup, comes across as more hostile than it should.