There is an article in the Washington Post about it

The scope of the intrusion, while broad, makes sense, analysts say, given that China wields great leverage over Cambodia, where Western officials say it is building a Chinese naval facility for the exclusive use of its military. The facility would become China’s first such overseas outpost in the Pacific — a significant element of a strategy to build a network of military facilities around the world in support of its aspirations to become a true global power.

"As China and Cambodia continue to deepen their cooperation, it becomes all the more important to China to collect intelligence on Cambodia,” said Joe McReynolds, China Security Studies Fellow at the Jamestown Foundation. “If you’re [Chinese President] Xi Jinping, the last thing you want is to be blindsided by political developments in Cambodia.”