I agree that the story is perhaps less important than an in-depth account of the DPRK's human rights abuses would have been, but I have serious doubts that millions of people are persistently imprisoned. What is your source?

WP claims "150,000 to 200,000" political prisoners. Given a population of 24 million, of which over 1 million are in the army, and given the high mortality rate in political prison camps, I agree with you that it's very unlikely that the number is in the millions.

Excepting if you consider the whole country a prison.

I think the article sufficiently demonstrates the relevance, interpreting this as a rare glimpse of the habitual censorship used to misinform the people of NK.

Agreed... The change isn't even significant