Grugq is well known in the infosec industry and more experienced in the area than you realize. He's been writing about opsec for years, among other areas.
I would wager anyone with intimate knowledge of how the KGB works, and has the evidence to prove it probably isn't going to be writing publicly about it for very long...
Forensics and attribution are big parts of the infosec world. Researchers study attacks, tools, payloads, etc. and get an idea of different threat actors, their levels of sophistication, and who might have done which one. I’m sure it’s never ironclad - the conclusion that it was a particular intelligence agency is just an educated guess, and sophisticated attackers might intentionally ape the signatures of others. But it’s not completely hopeless.
