Leonardo, you're correct if you go for the purely scientific aproach, but as Abramelin said, he posted this more as an appeal to ones imagination, as opposed to saying that it was the truth. He even says it is science fiction.
It's just a possiblitiy, a civilization whiped out by time, a long time. No remnants will be discovered for the strong sea currents in that area will have whiped out anything that might give us a clue. These same currents will have flushed the top soil, and only leave an ancient, 24 millions year old rock bottom, the bootom they took samples of.
Great , eh?
This said, who said that only hominids ever went up the long road to inteligence? I'm fairly sure that nature had previous (if unsuccessfull) tries. Who knows, maybe maybe there was a race of nearly intelligent insects or dino's a few million years back. The odds of finding evidence of that are next to nill.
I find that the beauty of the imagination.
Just see this as an excercise of thinking waaaaaay outside the box