I have some serious reservations about some of the facts in that article.
According to the video embedded, the transmission was "10 days ago" at "1245 AM". This article was posted on March 12, 2017. So the date of the transmission was around March 2. The closest Pyongyang numbers transmission I know of was on March 4, at 1515 UTC. They keep a regular schedule, the first and third Saturday of the month, starting at 1515 UTC. They used to also send on the second and fourth Thursday of the month, starting at 1615 UTC, but that cycle appears to have been dropped in late January, 2017.
The person who supposedly decoded these transmission appears to be in Britain, and the message traffic was purportedly about a British and American targets. But, these transmissions cannot be heard in Britain. Radio Pyongyang, the source of these transmissions, uses MW, VHF, and HF frequencies, and transmits these messages simultaneously on over a half dozen freqs. But the HF freqs are 3250, 3320, and 6400 kHz, and to the best of my knowledge these freqs have never been heard in Britain at the time numbers are transmitted, in fact they are seldom, if ever, heard in Britain at any time. Normal propagation conditions just don't support it. North Korea does have other shortwave outlets that are often heard in Britain, but the freqs and programming that carry the numbers transmissions are regional in nature and difficult to hear in Britain.
The person who defected, in Britain, and helped decode the message defected in August of 2016. He happened to have had the code keys to a message that would be sent for Asian reception 5 months later?
Of course, it is all possible, but there are too many holes in the story for me to take it seriously. Maybe the details were left out because they would have been tedious to the average reader, or to reduce the word count. And then again it would not be the first time a media story took a basically correct fact and presented it in a screwed up way that presented some of the facts wrong.
T!