Not really my area but I've been down a rabbit hole on this lately after someone in the UFO subforum mentioned it in passing. The railroad thing does keep coming up, especially in American reports. Old disused lines cutting through woodland, liminal spaces basically, seems to attract a lot of weird activity in general not just Dogman stuff.
My gut says its more about the geography than the rails themselves. These lines were built through remote terrain specifically because it was empty land, so you've got dense forest, wetlands, isolated locations all following the same corridor. Course thats also prime habitat for something large to move through without being seen.
Does anyone have specific locations where this pattern holds up? I'd want to look at whether its clustering around active lines, disused ones, or both before drawing any conclusions. Anecdotal patterns are interesting but they fall apart fast without decent data behind them.