User blog comment:FairyRaven/Fairy Tail Chapter 408: The Definitive Demon, Review and Commentary/@comment-24277053-20141110135803/@comment-7418318-20141111010847

Could it be possible that a part of Silver transfered into Gray along with the magic and that this is how he gained the knowledge he shouldn't have.

Apart from knowing about Tempesta and Minerva, Gray also shouldn't be able to just use his new power with perfect proficiency right off the bat without any training either, but he somehow does it anyway.