Interesting pattern you're raising here. I don't follow Dogman as closely as I do Mothman but the railroad connection is something I've seen come up repeatedly in the Mothman literature too - Point Pleasant being the obvious example with the TNT area and surrounding industrial infrastructure.
My working theory for years has been that these old lines create natural corridors. Abandoned tracks run through undisturbed woodland for miles, minimal human foot traffic, often following river valleys. Whatever these creatures are, if they exist and are flesh and blood animals, they'd be using exactly that kind of route for movement. Makes complete ecological sense.
The older the line the better apparently, at least going by the reports. Pre-1950s construction seems to come up most often. Anyone cross-referenced the specific lines with historical usage patterns? Would be curious whether the freight routes are more represented than passenger lines. Feels like the kind of data someone with more patience than me has probably already compiled somewhere.