I think it's a joke, this is the text that Facebook puts at the bottom of some false information.
As with all jokes though, I think there's an element of truth to it. May not be independent fact checkers, but discussion in this thread covers the iMessage comparison and I wouldn't say it's as clear cut as Zuckerberg would like to make out.
I don't think that statement refers to rust at all. It's just referring to the fact the software is open source and the user's data doesn't go through a third-party
[0]: https://www.gnu.org/music/free-software-song.en.html
[1]: https://www.youtube.com/watch?v=9sJUDx7iEJw