The Nephilim were on the earth in those days—and also afterward... Gen 6:4
That is the only clue that I see.
There’s probably some other theories out there.
I guess it’s not something worthy of in depth study.
Suffice to say that, we are ‘aware’ of their presence.
God bless!
I do not believe that there is any reference of angles possessing people in the Bible. It does state in Jude that the angles that left their first estate (life form) are now in chains in Tarsus I do believe. These angles left their spiritual bodies and took on flesh so as to mate with the daughters of man. That was their great sin taking on flesh and that is why they are in chains.