I see. So, what was the situation in Genesis 6:4?
Exactly, what Rabbi Skobac described in his video.
(נפלים) - Those were failing and causing others to fail. I.e. they were not keeping the 7 mitzvoth and were destroying the integrity of the world. There are sources that say that there was a rise of water levels, at this time, that destroyed a number of locations. I.e. as if nature was reacting to their actions and it would have been expected that the later generation of the flood would have paid heed to this previous situation.
(בני אלהים) - The descendents of power men. The leaders of the generation. The judges of that generation.
The above is according to TorathMosheh commentators Aramaic translation of Onkelos, Rashi, Ramban, Ibn Ezra, etc.