[Kölliker mimics Luca's excitement, continuing to burble. She's excited to meet blue small round, and talk to loud box dad! The word "bastard" is probably also thrown in there somewhere. It's fine.]

Well, at least according to the PokéDex. For example, sometimes Pikachus will emit a sound similar to the word "Pikachu" out loud, or any other derivations of that word. This phenomena is not limited to Pikachu, though I imagine different species have varying rates at which they communicate this noise.