The bubble being a new experimental interface being tested by a selected group of players implies the existence of an old established interface being used by everyone else for the last
seven years, no? So there are many other players, but we don't know which (if any) of the people the infamous five have met are player characters.
About the current meeting: it could be that at least one of the participants is a player, or it could be yet another thing happening
outside Dedalus's control. Game worlds achieving independence from their creators has been done before, see e.g. Kevin J. Anderson's
Gamearth trilogy. Virtual reality worlds going out of control has also been done before, as in Zelazny & Lindskold's
Donnerjack.