Technically only for non-classified internal communication. Classified stuff is restricted to be discussed only using military approved locked down hardware. But still, issuing a strong recommendation for Signal above all other options when communicating using regular devices is a good thing. Lots of "regular" conversations can still leak more than you expect through metadata, timing, etc, so they trust Signal to protect that
I mean beyond everything else, any group actually interested in the safety and security of citizens (so, not politicians or cops anywhere apparently), should be pushing everything to be encrypted everywhere. In the modern digital world anything not properly encrypted is at risk for ate tracks by bad actors.