I can't entirely say that this fail rating is incorrect, but I think it is important to take into account that Mugen Train is not meant to be self-contained. While it is a complete story, it's only one arc of the series. Nezuko's tendency to be in a wooden box, as well as wearing a gag, is explained further much earlier in the series, and if taking the entire series into account, it easily passes the Bechdel test. I simply think that that's important when looking at what not passing the test can imply about the writing.
In essence: While the movie doesn't pass the Bechdel test, it's a snippet of a larger story that easily does.
i can concede that there was one scene in tanjirou's dream where his sister says "i want rice cakes!" and his mother replies "then you can have some!" or something like that. and i can concede that these characters have known names in the demon slayer universe, but i wasn't able to catch their names despite watching like a hawk. so i would give this a "no".