User blog comment:IamJakuhoRaikoben/Chapter 445: The Ugly Fairy, Review./@comment-24228963-20150718064255/@comment-9595671-20150718194950

Yeah, since it said Igneel wasn't able to kill him, that doesn't mean he lost either. Considering we now know Natsu and END are the same being that seems to make it sound like Igneel fibbed the result to protect Natsu after choosing to raise him.

One thing I've noticed it being unable to defeat and unable to kill don't always mean the same thing. You could beat a powerful enemy, but simply be unable to kill him for reasons like he/she managed to escape right as you were going to deal the final blow.