Ovinomancer
No flips for you!
Good grief. The kobold was successfully intimidated. The players succeeded. The intent of the players is clearly not to alert the encounter to their presence, but instead gain information on that encounter. You're narrating a fail to that intent because the players succeeded. This is absolutely story curation -- you feel that it's a better story for the kobold to act out after being successfully intimidated, so that's what you narrate. You've obviated the play of the players and substituted in an outcome based on what you think the story should be. This is absolutely story curation, and if you're arguing from this being okay, then I can see why you think all GM narration is story curation. There's other ways to do it, though.No there isn't.
In both situations the GM makes a choice about the direction of the story. I could just easily frame it as the GM thinking that cowardly and possibly not so smart kobold could easily panic and the dungeon is filled with denizens so it is likely that someone would hear, but because the story is kinda dragging and the characters are low on resources they let the kobold to remain calm and offer useful information so that the story can progress smoothly and we get to the climatic end battle before everyone gets bored. One option isn't any more 'curation' than another.
Since the kobold has been successfully intimidated, the players get what they want and I, as GM, do not thwart that. This is not story curation, because I've following play and honoring the success on the tests I've called for. My narration is not in service to what I think makes the better story -- we've already established that the GM is concerned that this will make later encounters much easier due to having more resources available. The GM can think this even if not engaging in story curation -- they just aren't going to do anything about it by forcing outcomes, like a screaming kobold, to correct for it.