Moreover, Zhou Tian had a fair estimate of what the Dwarves were like: obedient though they might be to his commands, they would certainly not be able to work calmly if an NPC army was bearing down on them. Therefore, even if it was just to ensure the dwarves worked for him peacefully, or to keep the NPCs at bay, he had to step in himself.
Fortunately, despite the task being a bit tricky, Zhou Tian was confident in his abilities. Hence, even though he knew the NPCs were serious about reclaiming Mine Mountain, he was still confident in himself before any confrontation.
Consequently, before the NPCs could initiate their charge to reclaim the mines, Zhou Tian had already descended the mountain of his own accord.