The Mountain Opening Curse is considered another usage of the Earth Travel Technique.
The Earth Travel Technique forms a layer of True Qi around the body to specifically separate earth and stone, while the Mountain Opening Curse can remotely separate earth and stone to create a space or passage.
It's somewhat similar to another usage of the Water Avoidance Technique: the Water-Splitting Technique.
One is passive influence, and the other is simple active manipulation.
These are all secret spells, and although Lu Zheng's relationship with the Lu River God's Mansion is good, he was only given the most basic Water Avoidance Technique because of the gift of a Fish Leaping the Dragon Gate glass ornament at his wedding.
More advanced water control techniques like the Water-Splitting Technique were never mentioned.
