Indeed, the Burning Squad behind Zheng Jiawu controlled a Source Energy Stone mine vein, a deduction Gu Ran made on his own, rather than information voluntarily disclosed by Zheng Jiawu.
Don't be fooled by how mystical it sounds; in fact, it's not that difficult to figure out. Many forces have some Source Energy Stones, but they don't have many, usually just a few hundred to a thousand at most.
The origin is quite simple. For instance, when Gu Ran initially led the Blood Wolf Army to wipe out a small Jackalmen bandit camp, they found two boxes totaling two hundred Low-grade Source Energy Stones in their camp. If small Jackalmen bandit camps have them, it's natural that other small monster tribes and camps might as well.
