User blog comment:IamJakuhoRaikoben/Chapter 294: Battle of the Dragon Slayers, Review./@comment-12464349-20120805043319/@comment-4829046-20120807025239

They simply said that The guild became top after 5 mages joined it. Just because they are the top of the guild doesn't mean they are S-class. Maybe they didn't pass the exam.

Also from the way Mashima trolled Rusty-Rose we will see a similar thing with Rufus. He doesn't take the whole "being able to create anything you want" very seriously.