They'd be much more likely to use S/MIME than PGP, if they were going to use anything. The infrastructure for S/MIME is already deployed in much of the Federal IT space, while PGP is only used for some small niche applications as far as I'm aware.[1]
But that wouldn't have been a guarantee -- the message wasn't intercepted in transit, it was apparently intercepted by compromising the receiver's account. It's not clear how this was accomplished, but if it was by a trojan it could easily have end-run the message encryption, had it been in use.
Honestly, the security at most large organizations is so bad, they're not even at the level where their lack of email encryption presents the weakest link.
[1] Actually the only place I've ever seen a PGP key used in connection with a Federal agency, was by the NSA for reporting SELinux bugs / vulns. And that was a long time ago.
But that wouldn't have been a guarantee -- the message wasn't intercepted in transit, it was apparently intercepted by compromising the receiver's account. It's not clear how this was accomplished, but if it was by a trojan it could easily have end-run the message encryption, had it been in use.
Honestly, the security at most large organizations is so bad, they're not even at the level where their lack of email encryption presents the weakest link.
[1] Actually the only place I've ever seen a PGP key used in connection with a Federal agency, was by the NSA for reporting SELinux bugs / vulns. And that was a long time ago.