An anonymous source tells Radio Free Asia. All the articles about this site that source and sorry but not sure a US funded news org specifically made to put out stories like this is the best source of info.
If North Korea wants us to know something different, they could tell us themselves. Or, even better, let the people talk to foreign journalists without handlers and threats of repercussions.
Otherwise, we're forced to wonder about how weird it is that it seems like every news organization in the world is dead-set on spreading lies about this one, tiny, geopolitically insignificant country (and no, being able to launch toy rockets into the ocean once every couple of years does not make them geopolitically significant). Like, why did the BBC and RFA and Reuters and the AP and Al Jazeera all get together in a dark, smoky room and cook up a conspiracy to defame North Korea, of all countries? Why not, say, Thailand, or Malaysia, or Morocco, or something?
If you hear of a reasonable source with actual info on North Korean news, leave a link here. Otherwise, your concern is noted. Believe me, in the face of radio silence, most people are imagining much worse things of the regime than a shorts ban.