If you look at the Dong-A Ilbo report, it seems like they got angry while drinking and declared martial law.

On this day, the emergency order was made by Minister of National Defense Kim Yong-hyun and President Un.
It was reported that this was accomplished after a suggestion was made to the Ministry of National Defense.
After discussions with the above officials and a very small number of advisors, the President
This decision was made suddenly, and the drama was held in the President’s office from around 5 p.m.
It is said that preparations for the statement were made in response to corruption.

C: The content of the statement was announced to broadcasters around 9:50 p.m.
A message saying that you would like to connect to a live broadcast is displayed without guidance.
After being kidnapped, the situation unfolds rapidly.