Obviously I don't know your partner, and so can't comment on your personal surprise about what they said.My partner is an absolute TTRPG noob.
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They wanted to try GMing. I recommended Fabula Ultima's Press Start, since it basically doubles as a tutorial for GMing and learning the game.
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When we finished, they were surprised by how time flew while they were having fun. Naturally I was curious about what they thought about GMing, Fabula Ultima, and how things went. I was personally surprised by their feedback as the first thing that they said was that they liked was players coming up with things about the world during play. (This is part of Fabula Ultima's Press Start and how the game is supposed to be played.)
I didn't expect that answer because it's not a TTRPG topic that I have ever talked about with them before. They weren't using the vocabulary often used here of player-authored/generated-fiction or related jargon, but they were clearly talking about the general idea. They liked that it made things surprising for them as a GM. They liked what the players came up with, and they liked working that into the game as we played.
But the general character of what you say in the passage I've quoted is not surprising to me, in the abstract. What I enjoy about GMing is being surprised, enjoying what the players say, working that stuff into the game. So I can easily imagine someone else - like your partner - enjoying that too!
I'm glad your partner has found a system that works for them in this respect.
I do feel sometimes particular preferences or experiences are presented as norms. Sometimes rather dogmatically.I do sometimes wonder if we are conditioned by D&D and many other more traditional TTRPGs about things like GM/player roles with generating fiction.