Actually, no. It was very explicitly defined. Sean Murray, right up to days before the release, made explicit, yes-or-no responses to things contained in the game. Almost all of which were false. When things started turning out to not be in the game, such as multiplayer, he pretended it was a "bug" that people couldn't see each other - even though it was demonstrably not supported, including there being no real-time network traffic and no player models in the game files.
It's not a case of "buyers filling in the gaps". It's a case of the developer deliberately trying to deceive customers about what the game contained. Including putting a deliberately long painful grind to reach the center of the galaxy, and telling people that all sorts of neat stuff was near the center, to keep them playing for long periods of time. A cynical individual would view that as them deliberately trying to get people to play for too long to get a refund.