If it was China or Russia and they planned to release the information, they wouldn't want anyone to acknowledge their connection to the hacker. Not saying it was them behind this, just that the hacker could have just as much motive to lie about it.
There were also talks recently that "NATO may counter cyber attacks with conventional weapons" [1], so hypothetical nation-state attackers would want to downplay their involvement.
I am sensing bullshit, I'm pretty sure a lot of countries in NATO wouldn't want to do that, and if a NATO country attacks first (or a country doesn't interprets a cyber attack as an actual attack), the alliance doesn't hold.
