If you end up with a draft of a short story or a few paragraphs of a typical UX interaction scenario, or a storyboard, or a little film of someone swiping on a screen to show how your App idea would work — you have not done Design Fiction.
What you’ve done is write a short story, which can only possibly be read as a short story.
What you should ideally produce is something a casual observer may mistake for a contemporary artefact, but which only reveals itself as a fiction on closer inspection. It should be very much “as if..” this thing really existed. It should feel real, normal, not some fantasy.
When the game developer Blizzard Entertainment decommissioned some of their server blades to be auctioned off, they turned them into commemorative commodities, adding an etching onto the metal frame with the server’s name (e.g., “Proudmoore” or “Darkspear”), its dates of operation, and an inscription: “within the circuits and hard drive, a world of magic, adventure, and friendship thrived… this server was home to thousands of immersive experiences.” While stripped of their ability to store virtual memory or connect people to an online game world, these servers were valuable and meaningful as worlds and homes. They became repositories of social and spatial memory, souvenirs from WoW.