First, mentioning Occam's Razor isn't really helpful in realpolitik discussions and certainly not helpful in discussions involving DPRK since they are well-known irrational actors. Occam's Razor only states that the scenario with the fewest assumptions is likely correct. That isn't really useful when your scenario involves an unpredictable state actor.

Second, if you need to set up a fall guy, then implicating a nation state as historically secretive, aggressive, and isolated as the North Koreans is actually a pretty good idea.

"Do something bad and blame the weird kid" isn't a new idea.

I don't know who did it, but both arguments seem plausible.