Perhaps the true answer has far surpassed Gu Chun's realm.
As for this painting, no matter where it is, Hidden Moth can find it after breaking through Tier Four. He Kao didn't go looking for it, simply because he had already acquired it before then.
This painting is not a Grotto Heaven Divine Artifact, nor even a Divine Artifact; if you insist on understanding it as a Grotto Heaven Divine Artifact, that's also fine. As for what it truly is, Gu Chun couldn't grasp, or perhaps Tan the Immortal didn't answer.
This painting was passed on by Tan the Immortal to his disciple Leidunzi. At that time, the painting had only landscapes, and later Leidunzi added Tan Ancestor's image in the blank space.
The information Gu Chun received during worship could only roughly clarify things for He Kao.
He Kao asked puzzledly, "Why would Thunder Ancestor add Tan Ancestor's image to the painting, then let it wander the world?"
