There's some surprise in the media about ordinary North Koreans bursting into spontaneous tears when learning about Fatty Kim's death. But it's not at all surprising; propaganda aside, it's an incredibly nerve-wracking event. North Koreans in Beijing are talking about having to go back for the funeral, and not being certain of when or if they'll be able to return. Fear is as powerful a motivator as grief here.
Plus there's a lot of social expectation. There was plenty of weeping after Mao's death, but a significant proportion of it was because of the fear of what might happen if you weren't seen weeping. (Contrast with Zhou Enlai, where the grief was both more hysterical and more spontaneous.)