I'm probably talking out of my ass, but i doubt the interest for trains is psychologically different from any other hobby or occupation. Try explaining a regular person off the street why Linux rocks and Windows is the antichrist, or the differences between anime styles each decade since its inception. You'll get looked at like a weirdo. And you'll do the same back when someone who's a real film buff puts you through the history of the western genre, what studios got left behind after the advent of color and the intricacies of filming equipment, for example.
What's "unusual" about train enthusiasts is that their object of interest is a part of ordinary life most have stopped noticing