User blog comment:Water Dragon Slayer Shawn/Theory on why Gajeel and Natsu couldn't pass Freed's barrier./@comment-76.187.75.31-20140627021958/@comment-4829046-20140627041155

He is talking about it cause it is a pending question still left unanswered and had no instance of being evident outside of Fighting Festival arc and most probably will be covered in the next arc of the manga.