The game was marked "complete" when it was completed (as in all originally intended features were complete, the storylines were completed, etc.). However, there have since been some "expansions" (think on the level of DLC).Wait... wasn't the game completed?
Also, the creator launched a poll as to what project people wanted him to do, next, and the overwhelming victor of that poll was to "continue Space Journey X." Since then, the creator has been adding even more events and new gameplay mechanics, incorporating some things he had been thinking about as part of a potential sequel to the game (such as the recent "away team" mechanic), and it appears as if he will be continuing to update the game as long as there is still interest. Where he eventually takes it (whether to basically add a complete sequel storyline or just to continue with a bunch of smaller expansions as he has been doing) does not appear to be fully decided, yet.