Thanks for this interesting post
The ancient telling of a "Great Global Flood" comes in the connection of the numerous cultural Creation Story telling.
We all live on the same planet Earth, in the same Solar System, in the same Milky Way galaxy and in the same local part of the visible Universe. These facts are embedded in the ancient telling of the creation.
The Milky Way contours are often mentioned in several cultures as "The Great River in the Sky" which "runs" all around the Earth up in the Sky. If having no mytho-astronomical insights, people and scholars have no other possibilities but to think of a literal flood running on the Earth, but in fact this Flood/River runs up in the Sky all over and around the Earth.
Links to read:
Milky Way (mythology) - Wikipedia
List of names for the Milky Way - Wikipedia
Creation Stores origin from the Milky Way Mythology and before its Creation.
In fact, the Flood Myth is not a myth but the natural and ancient way of describing the scientific and factual cosmos around us all.