There have been several mega-floods throughout history that wiped out regions basically as big as human civilizations traded at the time. They were caused by various fallout from the ice age ending. Even some in North America. These are MASSIVE, once every ice age types of events. Humans didn't manage to keep much between ice ages, and that's if you take the evidence that humans have even existed as homo sapiens that long.

One example is the Bonneville floods. Thousands of years of erosion in days' time. There is evidence for another similar event up by Washington. That's just two, in close proximity geographically. There is similar evidence over in that region of biblically sized floods. Floods that would put any weather related floods to shame by several orders of magnitude.

It's probably just a corrupted story of one of those events, corrupted into that one story of a rancher basically doing exactly the story of Noah (minus all the preaching and grand-standing) for his ranch, for one of those smaller once a thousand years type floods.