Some scholars give us a more literal and exact translation to this verse: "Then men began to call themselves by the name of Jehovah." Other scholars translate the statement in this manner: "Then men began to call upon their gods (idols) by the name of Jehovah." If either of these be the correct translation then the evidence for the so-called godly line of Seth is non- existent.
This is just as much of a stretch as the "sons of Seth/ daughters of Cain" theory.
To impose a human interpretation at the expense of the obvious meaning of the divine Word, is a rape of the biblical text.
Which discounts the possibility that the meaning of the passage may not be obvious.
Philo of Alexandria, a deeply religious man, wrote a brief but beautiful treatise on this subject, called "Concerning The Giants."
Philo was a hellenist. He certainly would have been familiar with Greek mythology and the stories of the titans. I wouldn't consider his opinions to be representative of Jewish belief at the time.
Nowhere before the 5th century A.D. do we find any interpretation for "sons of God" other than that of angels.
I've cited this one several times recently:
You are the sons of the LORD your God... (Deuteronomy 14:1)
Beleive me there were plenty of Jews during the intertestamental period (all of the essenes and others) that had no problem with this approach.