I love that that conversation establishes that Londo had never encountered that particular story before his heart attack, so could not possibly have been playing out a version of it in his own mind: it wasn't a shape of making sense of the experience that he could fall back on. It was either happening or it wasn't.

Yes, that's a good point! (But also, his actual experiences track with the folklore in a way that is once again plausibly deniable; it's reflective of the story, but it's not specific enough that it could only be the story. Again, very nicely done.)

I do think it's an interesting touch that Vir was aware of the story and apparently had it as an integral childhood experience, but Londo didn't. I like it as a realistic take on how unevenly folklore is distributed within a society (not everyone will have heard all the cultural stories!), and also a character detail as well, since I expect that young Londo was a lot less interested in paying attention to that sort of thing than geekier young Vir would have been.