User blog comment:IamJakuhoRaikoben/Chapter 518: Master Enchant, Review./@comment-125.212.122.49-20170121132827/@comment-1776824-20170121215741

Actually it was a fire magic spell, and it was stated to be by Natsu, who said he ate it thanks to his Dragon Slayer Magic. However, he also had minor injuries remaining from is just-finished his fight with Jacob, hence why he appeared injured after the heat blast. Nothing was inconsistent about that particular instance.