Doesn’t matter if you’re using a compromised device. Given the number of people in the group chat, that at least some of them were using personal devices, and all of them are high value targets… I wouldn’t be so confident that this chat wasn’t intercepted.

That makes no sense at all though, this would be the dumbest way possible to do that. If you’re going to leak something you don’t include a paper trail of high level people discussing classified information in ways that are neither legal nor secure. And especially to The Atlantic, they would never be the choice if this was intentional for reasons that should be obvious.