User blog comment:IamJakuhoRaikoben/Chapter 390: The Story of a Boy, Review./@comment-4489126-20140627133949/@comment-24066070-20140627152450

Or maybe Deliora lied and he never managed to obtain Silver's corpse. It could be that the original Silver tried to fight Deliora and shouted something like "I'm Silver Fullbuster and I won't let you destroy my village", so Deliora remembers what Silver looked like and had Lamy remodel his new form into the exact appearance of Silver (like how she remodelled Tempesta).

It could be his hatred of Ur and anything related to her drove him to the point where he was willing to impersonate those precious to them, thus having him assume Silver's appearance just to mentally torture Gray.

He may then have made up the story of claiming the corpse as his vessel, because Gray would be slightly less angry if Gray knows it's not the actual corpse of his father, but just a copied appearance.