I think Luna is canon. So what you gonna do about it ?
People Usually came up with the term "Fanon" for other people shipping because of reasons, for example The Anime/Manga still continue and they didn't seem to be together as a couple ( usually its need a confirmation from the characters itself for us reader to know that they are a couple or the Author give us an information on Author Comments), The Author of the Anime/Manga didn't say / show anything that they are in "fact" a couple at the end of story.
So All the Hints or showings feelings to that character that she/he likes are nothing when the Characters itself are not Together. Its called "Fanon" and the Ship hasn't been sailed ( still on progress or fail ). Its also a "Romance Troupe" cuz thats one of the important point to show to us readers so we knew that they are together, and when they are together its "Canon" and the Ship has Sailed ( success ).
So i can see why many "people" said that they aren't "canon" ( still ). but "they" also wrong for being rude to the shippers. Its nothing wrong for shipping characters that we like anyway