Grave of the Fireflies isn’t a Miyazaki film. Grave of the Fireflies was written by Akiyuki Nosaka, and the film was directed by Isao Takahata. When the movie was first released in Japan it was paired with a Miyazaki film - My neighbor Totoro - so perhaps that’s where the confusion comes from? :)
>>Grave of the Fireflies isn’t a Miyazaki film.
You’re right, I just assumed that if it’s produced by Miyazaki, it’s his work at least indirectly.