I’m not expert, but it seems like this person (these people?) were not terribly sophisticated.
…Users of the social media site Discord say an administrator of a closed group chat room, or server, called “Thug Shaker Central” posted hundreds of classified documents during arguments over Russia’s Ukraine invasion.
“…clues left online may help investigators narrow down the pool of possible suspects relatively quickly.” Notably, the Times says, “the intelligence materials appear to have been first photographed and then uploaded online, a kind of sloppy procedure”