They don't. With the "What Pokèmon?" option, you can ask for any pokemon you know the name of. However, I'm not too sure how Hoopa, Volcanion and Diancie came to be.
Serebii accidently revealed these pokemon on his website but all gave out was their types and capture rate (which i have no idea how he figured that out).He also revealed the description for the move Light of Ruin which is:"Drawing power from the Eternal Flower, the user fires a powerful beam of light. This also damages the user quite a lot."