Honestly, after all my effort trying to dig it back up again, I couldn't find the original source. But it was when they announced the new classes, they had said it as if it were two separate classes, and not one. But either way, if you've played through the story, I don't see any reason to doubt that it's 2 classes. Gunner already has an official guild, and has since 1.0. It's up in the Marauder's guild. The dagger class on the other hand has a "secret underground" guild, the location of which is shown to be down by the docks. Moreover, we were treated to a fancy little preview of what the dagger job will supposedly be like in one of the cutscenes. I really can't picture them adding a gun to this job that is already using 2 daggers.