He probably was bonkers as there is no evidence to support a worldwide flood!
Floo, you seem to make two completely unrelated claims here. Firstly, there are plenty of flood stories from a variety of cultures around the world, and evidence for several - even if they aren't
necessarily for a single worldwide event.
Secondly, you are talking with the benefit of hindsight which is a poor evidentary argument; after all, Noah was necessarily working before any event occurred.
Thirdly, you are treating the Biblical Flood account as if it was a historical event when it occurs in a part of the Book of Genesis that has been proven to have been written in the 5th or 6th century BC - so definitely not a historical record - and deemed by an increasing number of scholars (Biblical and otherwise) to have been a theological treatise on the difference between the Jews' own God and the deities of the Babylonians.