The article was pretty light on details, but isn't it more a case of "Not Hosted Here"? This is the only relevant parts I could find:

> We need to find a way to have an encrypted messaging service that is not encrypted by the United States or Russia

and

> The French government’s encrypted app has been developed on the basis of free-to-use code found on the Internet.

I'm hoping this means they are using a mature, open implementation for most of it.