I think that the ghosts could be a combination of both, but I'd lean towards them as spiritual presences reaching across spacetime. To me, the ghosts seem like the most transient, in-between figure: not alive but not dead either. Similar to the narrator's perspective in A Shrouded Woman. The ghosts are showing their historical presence to connect the parallel narratives. And the train station seems like the best place to have it appear. Train stations are symbols of transit, perpetual motion, and lines connected to each other, but also synonymous with gigantic crowds and seas of people. I think we've all had the moment where we think we've seen someone familiar in a crowd but we lose sight, or it turns out to be someone else; in this novel, this "someone" just happens to be the target of obssession, and a past and possibly fictional creation that they're never met for real.

Xavier