From a review of THE BURIED GIANT:
“Despite what you might read elsewhere, however, this is not a fantasy novel. It has very little of substance in common with “Game of Thrones” or “The Lord of the Rings.” Yes, creatures like ogres and dragons stalk its landscapes and some of the characters knew King Arthur personally, but “fantasy” is a contemporary genre that uses the form of the novel to deal with the material of pre-novelistic storytelling. “The Buried Giant” reverses that formula, using the structure of a medieval romance to explore the moral and psychological themes we’re used to seeing addressed by the realistic novel.”
So, the reviewer seems to be of the opinion and school of thought that fantasy is a juvenile genre, and any novel that explores “moral and psychological themes” must, by her definition, not be fantasy.