Science fantasy is an oxymoron. Star Wars is fantasy. Space fantasy if you want to be specific. The problem is people tend to equate fantasy to the past and sci-fi to the future, and see them as otherwise interchangeable. In reality, sci-fi is more like a historical story set in the future. It’s supposed to be believable as something that could happen in our world.
That is the definition of Hard Science Fiction. Most science fiction does not fit that definition. Arthur Clarke wrote hard science fiction. Isaac Asimov wrote what gets called soft science fiction. The distinction is scientific accuracy vs. science inspired. All of Lucas’s inspirations in the science fiction genre are soft science fiction (Dune, Foundation, Buck Rogers, Flash Gordon). The emphasis is not on science but on using what science can project to tell a story of adventure. Lucas sets his as a fable by placing it a long time ago in a galaxy far far away, but he is not the first to do that or the only one.