It means that the game gives players the illusion of being in a freeform galaxy which should be a roughly circular shape where everyone approaches the center from the edges; whereas the truth is that everyone has their own corridor in which they go straight and cross-player interaction would be simulated by instance sharing. Programmatically, the latter is a lot easier to implement.
Of course, this is inferred by daymeeuhn's comments and then by adding some more assumptions on top of it and should not be taken as fact.
This would also make the multiplayer idea make some sense, because they could control the rate at which people occupy the same area, instead of just leaving it 100% to random chance.