There is so much weird shit like that from the Bible (or the apocrypha). And so many people who eat it up.
“-im” is a Hebrew plural morpheme. The root “nephil” means something like bully or tyrant. Take from that what you will.
But, most of these crazies don’t care what the original text said. They read something that is a translation of a translation of a translation, and then they still think it is infallible, and plenty of ridiculous antics ensue. The understanding of Nephilim as angels or giants or whatever comes from one particular game of telephone played over thousands of years.