In my opinion there are at least two ways to interpret this: a) It's an unintentional opsec failure. Perhaps there was an address book collision with another intended user. Perhaps it was fat-fingered. This seems likely. b) It was an intentional leak. Perhaps overtly, perhaps covertly, by one or more of the channel members for unknown purposes. This seems less likely as there are better ways to leak with less blowbac…
Option (a) 100%. This is an abysmal mistake on the big stage for a bunch of new people on the job. That it is the intelligence community makes it feel so much worse.
Basically a journalist was added to a discussion group of high ranking politicians.
This journalist is well known within those circles and has plenty of access to those people regardless.
The conversation may have been war plans, but the action is pretty uncontroversial across both parties, and went off without a problem so the impact of the leak was nil.
Seems like a great topic for making political hay, but twins that a mistake that can be easily corrected.