"A blade forged of the blood of my prey" does not necessarily mean humans!
the Chosen One runs off to a become a butcher while the apparition sputters angrily -- Gallifreya
Prophecies are funny things. When a child is born, they are lucky to get a prophecy that seems straightforward enough, until the inevitable twist at the end. A son prophesied to see the end of his father may only be there to witness those final moments, but if the father attempts to kill the son first, they set off a chain of vengeance that results in the same thing.
Therefore, when Bon was prophesied to forge a blade made of the blood of his prey, people around him naturally thought that he was going to become some conquering destroyer. So when the phantom came to tell him the prophecy, Bon came to a similar conclusion for all of five seconds.
Then he remembered that wording was important with prophecies. "Can I have that again, please? The exact words?"