This was released as a separate movie by Netflix.

It's a Special. Netflix has 3 categories. Film, Series and Special. This special episode was released in the Special category. You can list it as a film but that doesn't change the fact that it is also a special episode of the show and should be listed with the show in the Special Season folder. Why not update your database to be able to list such special episodes both in the movie and the tv show category? Because that is what those specials actually are. They are movie length special episodes.