This news article describes the opening of the trolleybus in Kumgol.
Within the article, the phrase 해주 appears a number of times, which the authors of "North Korean Surprises" (Tarkov and Merzlov) appears to have mistaken for a trolleybus system in the city of Haeju. However, this phrase can also be mean 'to do', which in this context, referred to the opening of this trolleybus system.