This is a product of their internal politics. The guy who was killed worked for the area that launched satellites. He thought there is no further need for belt-tightening. He distributed extra rations and that was considered a crime against the party. He said,
We no longer have to suffer and tighten our belts to make rockets or nuclear weapons.He gave instructions to send out 1 ton of fuel, 580 kg of rice, and 750 kg of corn to military officers at the Launching Station and their families.
[That doesn't sound like very much]
This was considered an anti-Party act violating the Ten Principles for the Establishment of the Party's One Ideology System.
He was feeling too good too soon about his world changing for the better and that's destabilizing. We're told all the anti-American posters were taken down. To keep power they have to keep everyone in line or the changes will be chaos.