I was surprised to see it too, but I suppose religious communities could be considered fandoms in a way? That word... does not come to my mind personally when I think of describing religious communities, but it is a group of people who share activities and interests, so I can see how it resembles or can overlap with fandom, or at least why someone in fandom might consider it similar to their fandoms. I guess that might be why OP shared it here, I really don't know. We've had secrets related to religious subjects before and figures from religion, so I guess a secret about religious practice isn't totally out of the box? It's focused on their singing hobby as well as their religious practice, which may be why it is fandom. I don't remember if we've had similar secrets to this or not. I'm honestly just thinking out loud here. If OP stops by this comment thread I would be interested to hear their thoughts.