Where did the other flood myths come from?
Flood myths originate in societies that live along rivers. Rivers flood. Wait, it might be clicking in there somewhere. People back then tended to concentrate populations near freshwater sources… those sources had a tendency to flood. People pass along stories about big events, like oh say, floods. Wait… wait for it. Those stories develop, things are changed, a story is added to the flood to give it more meaning to a people that didn’t understand why rivers flood. And then they copied Noah’s flood story before it happened.