They mean that the game avoids letting the player realize the distinction exists; they go in and out of multiplayer "mode", presumably based on areas or turns or something, and are none the wiser. All multiplayer/singleplayer scaffolding occurs occur solely in the background

IE the souls series, and its invader system.

[edit] just read the article properly, it looks like they really wanted it for is seamless transition between "p2p bubbles", so you probably enter singleplayer when waiting for the connection, and you've got a wifi-like connectivity problem (but due to virtual land movement).

So its not at all the issue of always-on multiplayer in general mmos; its more like guild wars "instances", and making the grouping automatic and no-felt-loading.