Life from another place (be it planet, dimension or whatever) doesn't only belong to a single term like "science fiction".
What is a space alien? Life from another planet? What if those same aliens were from an unspecified place? What if they traveled through what seemed like magic portals? When does it become "fantasy"?
Is Dr Strange fantasy or sci-fi? What if the elves traveling to Valinor in lord of the rings and the undying lands beyond was interpreted as off middle earth and therefore could be in the stars. Does Lord of the rings suddenly become sci fi? How about a story like Hellraiser? The Cenobytes travel between words though a puzzle cube? Sci fi, horror, or fantasy?
Listen, this seems like an unnecessary distinction, but consider one of the key figures involved in this thread, Kojima. This point might be of importance to him considering his last major project was under a genre he coined a new term from. He wasn't content to just say his project was a third person action adventure stealth game. It was a strand type game, a game with all those features but in which players affect each other without playing directly with each other. Most people wouldn't get much flack for saying everything with an unknown life form is science fiction generally, but it may be helpful to avoid immediately categorizing all media into exceptionally broad categories because of a single aspect.
