An early bible had the Galactica finding a derelict ship floating somewhere in space. I wonder if that concept developed into this concept...
While we're at it I have a question: we're the Cylons robots, lizard-men, or some sort of cyborg? In the TV show they lion like robots, & most people today say they were. But most contemporary marketing material called them lizard men. Cyborgs would be a nice half-way point, & a scene in the pilot's novelization has a Cylon undergoing surgery to add a third brain, which sounds like something a culture of cyborgs might do.
Here's an article for you.
https://en.battlestarwikiclone.org/wiki/IblisThe body found in the ship was likely Iblis' old one killed in the wreck, he may have possessed a survivors body and transformed it into his own likeness.