According to South Korea's Yonhap News, Kim got heated up after seeing a broken-down Japanese car blocking the road outside the Kumsusan Memorial Palace, the resting place of his father’s embalmed body. Upon seeing the car, he then ordered the law to confiscate most of the Japanese cars in the country. Vehicles used by some government officials or given to film stars (obviously) and athletes escaped the ruling.
Unfortunately for Kim most of the cars in North Korea are Japanese, which means it’s questionable whether the rule will even be enforced. Perhaps Japan could retaliate by seizing all North Korean cars, however, we doubt anyone in Japan would be silly enough to buy one in the first place.