You, uh, didn't turn multiplayer off in your options, did you? That setting doesn't follow your account around, it's per machine.
I leave it off on my laptop because it causes the Space Anomaly to devolve into single-digit frame rates when other players are present and rendered, especially when docking.
Note that this doesn't prevent you from seeing other players' bases, nor impact the ability to see people on your friends list or their status. Your game will still connect to the servers if it can. It only prevents other players' keisters and ships from being placed in your universe.