User blog comment:Miskos3/Fairy Tail Chapter 369: The Place Prayers Reach, Review/@comment-1359322-20140131120409/@comment-7418318-20140131122044

Considering how delighted he was about transfering the key, it looks to me as if the just experimented around and only found out how to do that right when he did it.

It'd be a bit risky to tell someone like Kyouka "I am able to transfer the keys" and then fail to do so, so he probably decided to keep quiet until he knew for sure he could do it.

And I think Zero waking up, without his seal being lifted and his terrible wound just disappearing would have been far bigger bullshit than revealing it to be an illusion. It might not have been the most spectacular or epic thing, but it was the logical thing to do.