User blog comment:PUNCHURPREGNANT/Gray and Silver Predictions/@comment-96.233.56.21-20140331020647/@comment-7418318-20140331084325

No we didn't.

But have you forgotten that Minerva is no longer Human either, even though she was born as one?

If she was turned from Human to Demon, the same may have happened to Silver.

But even if he was created from Zeref's book, that by itself still doesn't necessarily make it impossible for him to beget children with Humans.