I've noticed that the average horror story tends to be a fantasy story as well. Can you name any sci-fi creatures from a horror story? All I've got for now is Dr. Jekyll, the Invisible Man, Godzilla, Frankenstein's Monster, the villain from the first Terminator film, the Xenomorphs from the Alien movies, and the extraterrestrials from the Predator movies.
P. S.: Please don't quote Clarke's third law here; ignoring the gray areas of "science fantasy", there should be some distinctions between stories strictly about sci-fi and stories that involve some magic.