I have the same theory, but not about the creation story. Genesis 1 has so many global elements (i.e. separating water above and water below) and even solar-system scale elements (i.e. creating sun) that I'll count the creation verses as being global and not regional.
But my theory is how the word "earth" or "world" is used in the Noah flood story. Did the flood kill everybody except the few on the ark? Yes. Was everybody spread out all over the earth? I believe not. Therefore, the flood could have been a big ol' honkin' flood that wiped out all the people in the region (a legitimate definition for "world"), which is the same as wiping out everybody on the globe, but not necessarily be a global flood.
I base that theory on how the Hebrew word for "world" is used in other parts of the OT and all of us know it's not talking about the entire globe. For instance, no one looks at a prophecy of a conqueror taking over the world and says to others, "That couldn't have been Alexandra the Great. He didn't take over North America, which is part of the world."
I follow Dr. Micheal Heiser and he’s in the court that it could have been global and it could have been local. That is, he says the bible isn’t all that clear on it, and believers had better be careful about which hill they choose to die on.
I have a belief about it, but I’m willing to change that belief if more information presents itself.