The bible says the whole earth was flooded. Only trouble is we judge that statement by our own definitions. The earth was a very small place in the Bronze Age. The earth in the Gospels was the Roman empire (not the pagans, Parthians etc..)
We used to think the universe was everything there is - now we talk about many universes. That definition changed over 20 years. The bible goes back about 4,000 years.
In that case maybe there were other people outside the known world of the garden of Eden, and some of those people existed before Adam and Eve.