It is was understood as giant only because they didn’t really know how to interpret it and they based it on the words following. The same word not considering vowels means to fall or fail. It is most likely used as a title for those in the Garden story who fell as the’ Notorious’ ones, Cain was likely included among them.
The Sons of men would be Cain’s descendants and the sons of God would be Seth’s.
The old title forgotten, the term came to mean giants,
I agree that the **sons of God **(Seth’s descendants) are the
righteous and the
sons/daughters of men (Cain’s descendants) are the
unrighteous.
Adam was a son of God (righteous) before his sin and also again after he repented of his sin.
Luke 3:38 "the son of Enosh, the son of Seth, the son of
Adam, the son of God."
The “sons of God” were “giants” in that they were “men of renown” because it was obvious that they were blessed by God. They had many possessions and so they were noticed and admired by many people. However, it is possible that because of their intermarriage with the pagans and their adoption of their wive’s pagan beliefs (such as partaking of unkosher food and drink), that their unrighteous descendants gradually became “huge” as in giant-sized men. (For example: The Japanese were short in stature before WWII, but this is gradually changing now since they have adopted a more Western-type diet consisting of much larger quantities of meat/protein than previously.)
By the time of the flood, only Noah and his family remained righteous out of Seth’s descendants and so the flood destroyed all the evildoers while Noah and family were safe in the ark.
After the flood, there were again unrighteous giants:
Deuteronomy 3:11 “For only Og king of Bashan
remained of the remnant of the giants. Indeed his bedstead was an iron bedstead. (Is it not in Rabbah of the people of Ammon?) Nine cubits is its length and four cubits its width, according to the standard cubit.”
A cubit is about 20 inches in length. So his bed was about 15 ft. long and about 6.67 ft. wide.
Goliath was an unrighteous Philistine giant (huge man). Some Jews today believe that Goliath was a descendant/son of Orpah.
jewishencyclopedia.com/view.jsp?artid=336&letter=G