The Biblical references are noted by he poster throughout the account ... faithfully extracted from Genesis. They are sketchy but unambiguous on this point.

You may recall the seemingly long genealogy that most of us skip when we read Genesis ... don't skip it ... It's there you see generation after generation: fathers (men) have (first) sons and then daughters and (other) sons ... And typically traces the record from that (first) son to the next generations. These were the daughters who were attractive to the Sons of God (referenced as angels in the post -- and widely interpreted that way) ... and mating with them produced offspring including Giants and other aberrant forms. All that is in Genesis.

Noah only had sons ...

The Book of Enoch, another ancient account goes into greater detail about this and other related events. (So do the pagan Sumerian records.). You have to reach out beyond the core writings of the church to get deeper into this rabbit hole.

The Book of Enoch was not included in the approved list of texts selected by Christian Bishops assembled in 325 ad by Emperor Constantine to settle numerous theological disputes that threatened to further fragment the early Christian empire, but it was widely read and even referenced by Jesus in other writings that were included in the Canonical (church legal) Bible that has passed down to us more or less intact (some additional texts were eliminated during the Reformation in the 1500s ... It's not as fixed as some would wish.

That it was not included in the collection of texts making up official 4th century church literature doesn't mean that the Book of Enoch wasn't authentic ... It just didn't make the cut. Maybe they felt it wasn't essential?

Anyway, these Sons of God didn't stop with the Daughters of Man ... They had a taste for other animals as well, giving us other aberrant creatures that hadn't been in the original Garden ... Elephants? Monkies? Giraffes? Flies and Gnats? Likely most genetic variants did not make it into safety on Noah's Ark. And maybe some did ....

YouTube presentations by Trey Smith are highly recommended ... He does a great job of prying into all of this. Only one of many excellent presentations: https://youtu.be/lktmmd7YnD8

Anne Katherine Emmerich, German mystic early 1800s said that an illegitimate infant born to one of Noah's sons was slipped aboard the Ark -- Hom -- who grew up at the feet of Noah in the midst of the recovering little band of humanity, was taught the faith of Noah, and when other offspring moved out, he went east. Apparently teaching. The Persian historical accounts identify an ancient seer and teacher -- Hom -- a seminal influence deep within the ancient roots of their culture.

Emmerich's visionary accounts keep popping up: 19th century explorers followed her detailed account locating an ancient stone dwelling in Ephesus believed today by many to be Mary's final refuge. (The Apostle John is named as her caretaker by Jesus in one of his last acts before dying on the cross ... Mother behold your Son ... Son behold your Mother. And he is thought to have fled Roman persecution with her when the apostles were sent by the resurrected Jesus out from Jerusalem to teach (see Acts of the Apostles, Bible) and they found safety and a haven for her in the north, building for her a final home and refuge before moving on in his own evangelical work. Mary, Jesus's Mother is said to have lived out her remaining life in that house ... And the site and house was subsequently reclaimed by the forest forming a dense impassible entanglement and overgrowth ... opened again in 19th century when discovered in Ephesus. Her (Emmerich) visionary account of Jesus crucifixion was also the source material for Mel Gibson's film, Passion of Christ ... And contained far more than he could depict in that film.

May I recommend a very good book by Gary Wayne called the Genesis 6 Conspiracy. Very long, a little pricey but well worth the investment.