As the East Sea Army retreated from the Fae Mountain Range after finding out that they were far too weak to deal with the Illusory Beasts, Xuan Hao was silently observing the teleportation formation that was slowly forming beneath the old man in the Earth Immortal Realm.
Given that his understanding in formations was extremely elementary when compared to the person who had set up the teleportation formation, the simple act of observing the formation forming allowed his understanding of formations to increase by leaps and bounds. Directly allowing him to break through to the Artisan Realm and make steps towards reaching the Master Realm in a short week.
Of course, stepping into the Master Realm by only observing the formation of the teleportation formation below was unrealistic. Even then, it did allow him to get some insights into the realms beyond the Master Realm when it came to formations.