Apparently, the game's profile says it is a fangame, but it really isn't. It was put on the official Nintendo website and was developed by Nintendo themselves, so why does it say it's a fangame?

I've got no idea. I know I don't have access to change it, it seems like a site admin thing.

You could request it get removed via support hub, I have done it in the past and they are more than willing to do it.