It's explained in the Article.
Hmm does anyone know why don't they use Signal? Signal seems to be more secure to me and has disappearing message as well.
I was going to ask the same
"The reason staffers are choosing Confide over other secure messaging apps, like Telegram and Signal, is that Confide deletes chats as soon as they are read. In other words, by default the app deletes messages after they are read. “We immediately delete them from our servers and wipe them from the device,” says Jon Brod, Confide’s co-founder and the company’s president.
The company deletes all messages from its servers and wipes them from people’s devices after they are read, according to Confide. However, other secure messengers, like Signal, do not wipe read messages, which mean that they could be interrupted if someone gains access to a smartphone where the messages have not been clearly deleted.
However, there are some security researchers who are doubtful about Confide’s cryptography bonafides, typically because the app is not open-source like Signal and may use old protocols."