Why does it say Poliwrath!? lol
Maybe like Anon?
Have you tried interacting with the boy? He turns into Zorua who will then join your party as long as you have an empty spot and a spare Poke Ball. Also make sure the Celebi you have is the one that was distributed to 4th Generation games during the Movie 13 event. If it isn't that specific Celebi, you won't get Zorua.