User blog comment:Derax-Pagani/Chapter 502 Review/@comment-62.113.23.47-20160917115449/@comment-5303512-20160917115946

Doubt it is a dragon, plus where that tumor was is the same location where Zeref pierced the book which effected Natsu too.

If Natsu had a Dragon form he had already shown it based on the second movie poster where he does Dragonize, but if you look he still had the bandages from the FDKM.