official doesn't mean it's not fanfiction. Fan fiction is just works that have characters or settings from other people's works. Literally no part of that definition excludes things made with legal permission.
And canon, likewise, has nothing to do with the original creator or rights to the series. Canon has to do with the generally accepted parts of the story, because it comes from the study of older mythology and literature. Lots of parts of the canon of King Arthur were written hundreds of years after the origin of the story, but are accept as part of the canon due to their ubiquity.
And because this is true, the inverse must also be true, things can be non-canon because they are generally not accepted as such