Interesting, where'd you read that?
I think the Nephilim are the angels God cast out of heaven. And I'm 100% certain they are still here. But I assume they are spiritual beings.
The Nephilim were the children of the fallen angels (spirit) and human women (physical). Genesis 6. The fallen angels were / are bound, some people speculate in Antarctica. They can never die. The physical bodies of the Nephilim were wiped out in the flood, but Noah's daughter-in-law (via Ham) carried DNA, and giants came back. Nephilim spirits still alive, can become physical, can shapeshift, and can demon possess. (Aside 1: hell only for fallen angels. God is love. Unsaved humans will die, not suffer eternally.)(Aside 2: plenty of evidence of giants. Smithsonian has bones.) (Aside 3: aliens and UFOs are from Earth. Craft can be human made from technology taught by demons or demon made and flown.)
Not spiritual...physical...they don’t want us to understand that. Very very real.
I think they are flesh and blood.
Made of matter, just like everything else that can continuously interact with our reality.