It is unclear whether or not the Headless Horseman was a real ghost or was simply Brom in disguise. The original short story written by Washington Irving suggests the latter more overtly than the film. The best evidence in the film to suggest that Brom pretended to be the Horseman is the similarity between the two characters horses.
The song "Headless Horseman" is considered one of the darkest songs written for a Disney film. It, much like "Worthless" from The Brave Little Toaster (1987) and "Hellfire" from The Hunchback of Notre Dame (1996), was nearly cut from the film.
During the live-action sequences in the library, the narrator mentions King Arthur and Robin Hood among other stories. Disney would eventually make these two with The Sword in the Stone (1963) and Robin Hood (1973).
When Brom Bones grabs the barrel of ale, the side with the corked hole is pointed away from him. When the camera moves to show him pulling the cork out it is suddenly facing him.