Remember this very carefully: a cult is a religious or quasi group the doctrine or practice of which involves some amount of secrecy.
Do you understand this distinction?
Oh, pure baloney. I understand that is YOUR stipulated definition, one that you wish to force on others. Sorry, but I will not accept you as a religious or philosophical authority.
So, let's examine YOUR little cult's definition. Since the Catholic confessional is secret, they are a cult. That's a practice that involves some amount of secrecy, as per YOUR definition.
Here's another definition: Cult is a word used to name a group. Some people use it as a pejorative; e.g.: All religions, except their own, is a cult.