There is no difference between a comet and a asteroid in this kind of situation, both would cause tsunamis. On the other hand, having a huge fireball in the sk

There is no difference between a comet and a asteroid in this kind of situation, both would cause tsunamis. On the other hand, having a huge fireball in the sky, earthquakes, ash falling from the sky, would probably leave an impression along with the tsunami (flood) that would be in the flood story. I seriously doubt the flood stories came from an asteroid or comet impact. Much simpler explanation is that it is a memory of either Black Sea forming or memory of the sea level rising at the end of the ice age.