Lost world revealed by human, Neanderthal relics washed up on North Sea beaches

Laymen were nor very aware of what was going on mere hundreds of kilometers away. It is very possible that either this meltdown or Bosporus overflow was interpreted by some as "everybody died".

It seems plausible that a relatively slow increase (that is, compared to a supposed catastrophic flood) over tens of years, well within a single generation, could turn into, "and the entire world flooded overnight" within a generation or two of exaggerated story-telling. I mean, most religious fables are probably nothing more than exaggerations of real events, if not outright fabrications.

That kind of increase might very well be noticeable from year to year, and after 10 years you might come back to where your lands used to be only to find the sea has taken it over entirely.