> The simple answer is that some storied reference events that happened that long ago.
This is another thing that you can't know.
If there is a match between an inferred geological event and a mythological event, you'd still have to ask "what is the rate of this happening by coincidence?"
And then you'd still have to ask yourself, whether anything is real or a simulation, or a dream of god, etc.
Otherwise history is indeed much guesswork, as we don't have a timemachine and rely on lot's of indirect evidence for everything.
Your mistake is leaning on the mythology, having, it seems, not actually listened to the songs and stories yourself, directly.
There is no coincidence - the song lines record real geological events, such as the lowering of the oceans, the formations of islands, the drying up of lakes - on an ancient timeline - all of which are verified in the geological record.
Please, do not lean so hard on the petard of treating this subject as one of methods and coincidence.
These are real cultural artifacts, which encode real events.