The leak happened earlier this week during a forum discussion regarding the T-90M, T-80BVM, and T-90S Russian main battle tanks, all of which are currently in service and appear in War Thunder itself. The documents shared are user manuals meant for those operating said vehicles and have, like most other military documents, been declared classified or sensitive even though they contain relatively surface-level information.
tbf, if I ran an intel agency, after all these incidents, Id probably have someone "leak" fake classified docs on the warthunder forums or other similar places once in a blue moon, to spread misleading information to rival agencies as to the capabilities of my nation's equipment. Both to blend in with a place idiots are known to actually post such info, and if its found out my agency was doing this, to cast doubt on the validity of any real docs from my side that were leaked before. Doesnt seem like itd cost much of anything to do, so there would have to be only minimal benefit to be marginally worth it
Good ol' Murphy's Law: the quickest way to find correct information is to post incorrect information on the internet and wait for the inevitable "ackshyually".