The current prevailing theory is that North Korea hired outside hackers for this job. That fits the level of skill shown (less than CIA-level, more than skiddie level), the damage done, and even North Korea's response (had it been homegrown hackers, I'm not sure Kim could have helped but shout it out to the world).
That is a rather difficult hypothesis to support. How do you show that the hackers were hired by North Korea? What would North Korea be able to offer in compensation?
Also, pointing out that an action was illogical in no way proves that it was not North Korea. They have shown time and time again to be a country that makes bad decisions, and acts with little regard for the consequences.
The third generation Kim is not quite the rogue actor his predecessors were. Jong-Un seems to be aware of the fact that his country is under a microscope now and that he can't always just do what he wants. Furthermore he seems aware of the fact that the support they used to enjoy from China is quickly becoming exactly that - support they used to enjoy. While not the most logical guy at the party, Kim Jong-Un seems to have a little more awareness of the world than what we used to see from North Korea.