It's a movie all about Halloween crossing with Christmas and thus is valid for either holiday and all the time inbetween
However, while it is valid for both, since all of its major characters belong to its primary setting of Halloween Town, I would say it leans harder in that direction.
It was even released in October directly preceding Halloween, so that tells you what kind of movie the studio believed it was.
Disney also converts their Haunted Mansion into the Nightmare theme at around the same time as their other Halloween decorations around the park.