Yes. A nonfiction story is a story that is not true.
A story becomes a fiction when the events in it are not true or imaginative by the writer.
If it is just a book with facts about Neptune, then its nonfiction. But if your book is a story, say, people go to Neptune and discover life there, that's not factual, so it's fiction.
A story that is true it is the opposite of a fictional story.
fictionalized history. but non fiction