Hi,
room and scenes are separated. a "room" is simply a virtual space where you gather users to play together, they can interact within that room, but not with players not within that room. That's how you can have multi games running at the same time, but players from one game can not see players from other games. think of a tennis game. only two player can play a single game. but many mayn users will play your game, the way to go is to create one room per game, with only two users per room/game.
now, within this tennis game example, one user might be already read on the court, while waiting for someone to join and play, and for this you might want to have two different scene, one for the menu, and one for the game. so both players are on the same "room" but in different scenes, and that's fine.
bye,
Jean