The mangas
aren't official Nintendo releases. In fact, they are only
licensed. Copyrighted. Nintendo has legal rights to the mangas, but they weren't created by Nintendo. They have been approved for profitable release, but have not been deemed official/canon. Akira Himekawa are big on ZeLink shipping and creation of original characters (Ganti, Raven, etc), but they are not at all employed by Nintendo. Basically, they got approval to draw their own adaptation of the stories.
Fun Fact: The Rito tribe was inspired by Himekawa-sensei's Watarara race.
Sound and Drama, on the other hand, is an official Nintendo release, right alongside the music of Koji Kondo. I'd stand to say that S&D is canon, but I'm not going to state that it's fact. It does, however, have more weight to it than Akira Himekawa's mangas.
Not trying to argue that S&D is canon, nor am I trying to argue against it. Just clearing a few things up.
I could create a manga and obtain the lincense through Nintendo (if they liked it enough), but it wouldn't mean it was canon.