Wow! Sorry the picture's in the wrong angle, but that is a cool Easter egg in Pokémon sun and moon :)
It even has a different music playing in the background. It's actually what you hear in a Pokémon center but with a music box playing it.
First, the room is dark, then boom! Confetti and Nurse Joy says happy birthday, Pikachulover!
Clever Easter egg, game freak