Even without things being crazy on any sort of global scale. The Nile floods all the time & any river that regularly floods may go many decades or even centuries between the most severe floods. The story of Noah is about a man who was "perfect in his generations" which probably means all of his family relationships where healthy. And because of that he knew to heed the warnings of elders & the family was able to work together against all sorts of social attacks to build the sort of structure that would ultimately save their farm. They acted on what they knew to be true, not with concern about what others would think. Through family cohesion & efforts to prepare themselves for the unexpected they survived the storm. And part of the message is also probably that people who seem crazy might be able to see something you don't.

Stories that get told over & over, & especially when translated multiple times (idioms, phrases, & literary devices for communicating significance rarely translate well) naturally end up exaggerated in a "telephone game" like manner. The message is what's important IMO.