User blog comment:IamJakuhoRaikoben/Chapter 390: The Story of a Boy, Review./@comment-24066070-20140627101308/@comment-7418318-20140627105711

Sure it was Lyon who thawed him out, but how would Deliora know that?

Natsu was the first person he saw and later Natsu also was responsible for thawing out the Sun Village (even though indirectly through Atlas, but again Silver/Deliora doesn't know that), so he might have concluded that it was Natsu who thawed him out, even though it's not the actual truth.

And that facial expression might also have been determination. Playing nice with Humans - beings less than insects according to the Demon's believes - can't sit right with him, but he might be willing to do it for the sake of his personal revenge.