Means North Korea didn’t do the hack. Could be a work for hire, but it’s not sourced by NK. Lots of people, who know their shit, have come to the same conclusion.
The established norm on these kinds of events is disclosure. It’s done so that everybody benefits from the understanding, and it’s done to peer review secure options and make sure they actually are secure.
When things are not disclosed, they aren’t trusted, often are nefarious, and there is manipulation going on. Back doors, exceptions, logging, and other kinds of activities are the norm for non-disclosed “secure” systems and events.
But it’s a lie associated with a corporation, and that pisses me the fuck right off. And it’s a corporation who has been shitty to ordinary people on a number of fronts too, and lax in their own information practices to boot.