To the North Koreans, it is beyond comprehension that people living in the US made something, rather than the US government making it. To them, if Americans made it, that means America made it.
This misunderstanding isn't limited to works coming out of the US of course. Another example of this failure to comprehend freedom of expression is the aftermath of the Muhammad cartoons published by some Danish newspapers. Enraged extremists around the world began rioting in front of Danish Embassies, as though the cartoons were drawn, commissioned, or even approved by the Danish government.
See also: The souring of Chinese-Norwegian relations after the Norwegian Nobel Committee (which is a private organization which awards a private prize, despite having some members selected by Norwegian parliament) awarded the 2010 Nobel Peace Prize to Liu Xiaobo.