There's a difference between Microsoft or Google or Symantec coming out and saying 'this was NK malware' and the CIA or NSA or FBI saying 'this was NK malware' - people would be more inclined to believe the former rather then the later, even though we would still have to imagine that it's possible they are saying this because of CIA/FBI/NSA influence.

Likewise, Kaspersky is more believable than if the FSB came out with this story, even if we must be cautious that it could be an FSB story.