User blog comment:IamJakuhoRaikoben/Chapter 356: Tartarus Arc, Review./@comment-5303512-20131019065631/@comment-7418318-20131019072228

He is really a demon and only appears Human.

Maybe he can choose how he looks in his Human shape (a bit like the transformation spell Mirajane used early in the series and in the phantom arc) and because he respects Gildarts so much (or simply liked his appearance) he copied his looks.