Have you ever considered that science fiction may not be a genre?
People are always looking for ways to categorise art, and to group together things they like and things they don’t. It’s quite natural for people to lump together all the books with common elements.
I don’t want to try to offer a definition of sci-fi, but in common use, “sci-fi” is applied to books with speculative technology like nanotech, spacecraft, AI, or faster-than-light travel, or alien worlds or characters.
Problem is, that doesn’t really define what the story is about; is it a slasher movie, like Alien; a horror, like Event Horizon; a fairy tale, like Star Wars; or a kung-fu move, like The Matrix?
What I’m really wondering is, if someone says they like Science Fiction, what the hell do they mean? Have they told you anything about their tastes?