User blog comment:Collbrande-Ex-Caliburn/Hyoudou Issei's Peerage composition hopes/dreams/hypothesis/@comment-26821288-20161228004608/@comment-9595671-20161229023235

Well nothing says Ishibumi didn't retcon Tannin's appearance either, for all we know he really liked how he made Grendel looked and figured there should atleast be one other Dragon that's bipedal so it's not completely odd, and it would be kinda hard to explain why only one dragon stands on two legs.