This certainly sounds like a sloppy hoax. But there is evidence of seafarers From the area we now call Tunisia visiting Papua New Guinea. They writings on the walls of a cave were then gradually covered by a transparent layer of limestone, the thickness of which allowed a rough lower limit of its age.
I read about this long ago so I may have some of the details jumbled. But the gist of it is correct for sure. Perhaps someone more motivated than I could track down the full story.