The Biblical flood was probably the flooding of the Black Sea, which happened at about the right time in a similar, but smaller event.

But there's also the flooding of Doggerland, even the flooding of Lyonesse (which some people think is Atlantis due to the similarity in names...much smaller event, though).

So...yeah.

Five million years ago is pre Homo erectus. It's unlikely that an oral tradition has survived through multiple species. Is it possible, though?

It might be. What's more likely is that the Black Sea event made people look at the straits of Gibraltar and go "Hmm...ya know, it looks like the same thing happened here."