There are a lot of other clues in the text. For instance, the verse about Noah saying he was perfect in his generations. Christians often think that means he was perfect, but we know he wasn't because he got drunk and cursed one of his sons. What it means, I think, is that he and his family were genetically pure, ie untainted by all the Nephilim bloodlines that wreaked havoc with humanity and were probably the source of Greek mythology. This includes angelic DNA spliced with animal, by the way. How else do you explain the appearance of half-creature entities like minotaurs and whatnot, not just in Greek mythology but in ancient cultures across the globe (for instance, among the ancient Mayans, as well as Anubis and whatnot in ancient Egypt).