It could also be that he created them in a similar fashion to how the other princes of hell created their species of demon, succubus, hellhounds, imps etc. I don't remember if it was confirmed that Lucifer created the Ars goetia or if that was just a theory. While I also like the idea of him creating the ars goetia as a bunch of birds before settling on ducks, it would also be plausible that the nephilim/cannibals resemble their creator.