Was Noah or those who wrote about the flood, aware of what the Earth truly was? Or is it true that many ancients spoke of the world as to what they knew?
If we were to take the story of Creation literally, as if that was truly how human life was formed, is it even then logical to assume that in the short time between Adam and Eve being kicked out of the Garden of Eden, and the flood story that the entire world was populated? Not at all.
Then given the fact that there are two flood stories, taken from different sources, which are most likely taken from the Epic of Gilgamesh, included in Genesis, it is not reasonable to believe that they meant to make the story to include the entire Earth as we know it today. Couple that with the evidence of a localized flood, and the way that ancient histories were written, it is only logical to assume that it was a localized flood.
Yes, conservative Christians would disagree, but the fact that they are ignorant to Biblical history, as well what the Bible actually says means very little to nothing at all.