Possibly, but as I understand it, the fallen angels did the Genesis 6 thing over again, some time AFTER the Flood, when the population had become somewhat restored. That would explain David’s run-in with Goliath centuries after Noah’s Flood. The last giant named in the Bible was Og, king of Bashan. He was killed by Jewish soldiers, if memory serves.
You may be right, but if there was a second incursion by the fallen angels, (Numbers 13) to do the same thing they did in Genesis 6, I suspect it was another suicide mission, as they were probably locked up in Tartarus, as the watchers were. If indeed, that is what happened, I don’t think the outbreak was nearly as big as the first one. As in the days of Noah, I think means those hybrids are coming back, and may already be here.
As far as who killed Og? I had no clue, so I looked it up. It may very well be, exactly as you said. 👍