Thinking that it was just a one off claim in a single text was my initial suspicion here, as someone who knows nothing about the subject. If it’s repeated across other “texts” (didn’t they use clay tablets?) then so much for that.

Yep. I only learned about it last night, but there are many of these king tablets. They mostly agree with each other within a margin, which is interesting. So the scribes were getting it right, but whatever came before clay tablets (oral history probably) had already goofed it up.

Also, one of those early kings was also literally a well known god. So it's possible they were just saying "Before the flood Gods ruled on earth", and we've since forgotten most of those gods.