>> I'm not sure how I got that definition. I suppose 'vignette' is more
appropriate. <<

Yeah, vignette is for a fragment of something. It's often left to stand alone, but it really acts like a part of a larger work. Vignettes are great in fanfic or shared worlds where there is a massive canon that readers already know, so you can just write this one bit you want to explore. Outside of that background context, it's hard to make them work well. But they are good for crowdfunding, where you want to make a tidbit worth reading on its own, yet leave room for expansion.