I believe the logic is simple, the same as with advertising illegal drugs: lies can be seductive and do harm. HK officials make people consider any outer information as lies-filled propaganda, and thus justify the prohibition.
Not about to defend NK regime, but to make it fair, and not to play "they are bad guys, thus we're good guys".
First, doubts of people not right away believing any news about NK are justified, given how many lies about NK, like executing by feeding to dogs, were spread. So don't take them as NK defenders, it may be just a healthy skepticism.
Second, note that NK kills their citizens for what is illegal in their country, which is gross, but in 2019 Americans killed North Koreans for what was pretty legal, and got away with it [1].
Third, it looks hypocritic to read how horrible is that people got prosecuted for just watching videos. We all know that in so called civilized democracies, people's life can be ruined (luckily not taken) for possessing illegal video materials, it's just legality differs by jurisdictions.
West's true advantage is that we're much more shy in capital punishments, however we're still far from humanistic ideals, and I believe concentrating only on NK regime crimes lets the mindset "they being so bad, then we're not so bad after all".
You're not that old, are you? :) Before www, expect was the way to go.
<https://en.wikipedia.org/wiki/Expect>