Pool Party is a part of VMRP that happened.
Everyone on the good side is gathered in the Break Room, when the bad guys are still stuck next to it on Wolf's broken Arwing. Salmon sneaks into the break room and announces that she bought a pool for everyone in an attempt to make everyone more friendly towards each other. Everyone thinks that it is strange how she got to do that, but she gladly announced that she "borrowed" some of Espeon's money.
She tells everyone that her twin sister Cerulean (formerly Lumos) was coming to visit. She wanted a welcome party, and she could learn about the rivalries later. Wolf gets word of it and, while he knows that Zangoose would not have approved, joins in.
Salmon introduces Cerulean to everyone while the party is starting.