He was passing by when he noticed you battling another trainer. As the battle resulted in your win, he decided to come congratulate with you for your victory "The feelings you have for your Pokémon... And the way that your Pokémon gave their all in battle in response to those feelings..." Claps his hands and looks at you with a wide smile "Those two together created a great power. I hope to have a proper battle with you at the Pokémon League, one day."