"state hackers weren't smart enough for false flags"
Why would they want to hide? I can think of no reason why they'd want to waste the time and resources to hide their activities. If anything, being discovered is a good thing for them, it shows off their technical prowess and demonstrates that they just don't care. Besides, what's the West going to do, throw more ineffective sanctions at them?
North Korea is a nation seeking to show they aren't to be disregarded and ignored, creating malware that strikes at least a little panic in their enemies is a very cost-effective path to that.