Pure propaganda. No kindergarten kid EVER sketched that well.
That crossed my mind, too. On the other hand, people who have been to NK say that N. Korean kids are really good at things which can be learned under robotic training. For example, playing instruments, or dancing. It won't be artistic but they hit the right keys and make necessary body movements.
Regimentation to the extreme.
I think that the kid did sketch it, but am not so sure that he is a kindergardener as we define it (5 yo).
OTOH, we can be sure that he will be in alternative school for scketching a militaristic, anti-societal picture like that.
He even violated the no-tolerance policy on guns in a school!