I asked it for "hard space sci-fi", and it gave me a book about space (not sci-fi), a book about mental illness set in the ocean (I think? It was hard to tell), Congo by Michael Crichton (not space), and one book that might have been hard space sci-fi.

Edit: I asked it again, and got: a book about space, another kind of book about space (spacetime and geometry), a sci-fi book that definitely wasn't "hard" sci-fi by my definition, and a "Cat in the Hat" book about space. Certainly amusing!