Unlike in old times when formal passes were not invented yet, in modern rules there is a simpler reason (besides L/D confirmation) why the B stone cannot surround territory.
W can force him to fill sooner or later since every W pass threatens recapture. Even if B also passes to stop the game, W can just resume, recapture and force B to use up a threat each time. (IGS goes as far as not even stopping the game before the third successive pass.)