For many people it may come as a surprise that Star Wars is listed as “action, adventure, fantasy” on IMDb. That’s actually correct. It just doesn’t have the characteristics of sci-fi.
So, what is sci-fi? Its basically a “what if?” story. How does a certain scientific discovery affect the society or the people living within it? Its about speculation on human nature. It doesn’t necessarily have to have anything to do with the future as alternate history is a subgenre.
What is fantasy? Its about being cool. Its about people who are larger than life taking on quests of epic proportions.
Which one of these represents Star Wars better? Sure, the universe is technologically more advanced than ours in many ways (although they apparently lack things such as paper), but it doesn’t really dwell into why things are the way they are and how did technology lead into that. Instead, we get action set-pieces displaying how these people can handle anything.
On the other hand, we have a setting. Setting is simply the time and location where a narrative takes place. It is often closely tied to genre, because the setting often implies the mood. If you use a modern city as a setting, you expect a certain amount of realism compared to a setting with elves and dragons. Setting also often implies the story in various ways. If you put those elves and dragons into a modern city, it would be hard to get away with not addressing that in any way.
Of course, the problem with all of this is that setting is clearly defined, or can be clearly defined, whereas genre is a fluid, very abstract concept.
Why does this matter? First, when the GM is trying to sell their idea to the players, there is going to be a problem with the message if these concepts are not handled properly. That can lead to wrong expectations. If you just discuss your futuristic setting with players, they may expect a Star Wars -like adventure, or they may expect Star Trek -like exploration.
Fiasco has a pretty good way to approach this. They list a ‘Movie night’ in each playset, which gives you an idea on what the whole thing is about. If you see Star Trek: The Next Generation (not the movies) on there, you get a very different idea than if you would see Star Wars or Aliens. Similarly Lovecraftian horror is very different from Dog Soldiers, Descent or Get Out.
Good communication on what you are actually planning can be of great benefit here. You can’t just throw people into what they perceive as the Wild West and expect them not to plan for shoot-outs, even if you just wanted a family drama in an unusual setting.