Lunarians lived atop the Red Line well before the existence of Mariejois. If it turns out the Red Line is actually the "Serpent soaked in blood" that encircles the world like Jörmungandr (I literally just posted about this in the chapter discussion by pure coincidence) then it could well be connected to tales told in the Harley texts the first time "the world was destroyed".
Actually, it could well be in those ancient texts whether the serpent thing is true or not. All those ancient races are most likely connected if we go back to before the world was reset, and Elbaf is seemingly the place that has been able to keep its legends intact the most out of the current WG-led world.