User blog comment:FairyRaven/Fairy Tail Chapter 470: Hybrid Theory, Review and Commentary/@comment-1359322-20160125125836/@comment-9595671-20160125190455

Unless he didn't have Dragon Slayer magic back then. Since the Wizard Saints fought off screen, that was likely Serena's original magic he used to defeat them with.

When he used the Dragon Slayer magic, they all looked surprised. That could mean he didn't get any of those Dragon Slayer Lacrima until she switched sides.