User blog comment:IamJakuhoRaikoben/Chapter 313: Champion's Scenario, Review./@comment-4047931-20130105005727/@comment-5459029-20130105214003

Its explained how the keys returned to Lucy and Yukino. Loke can go out of the gate, and it was him who got the keys and return them to Lucy, You know Loke has the habit of going out of the gate without Lucy's permission, its possible that he just do that habit again and of course, he will go out of the gate near his key, so maybe he saw the keys and lucy wasn't therre, so he find her. :D