As he would have to expose the existence of the Library of Heaven's Path in order to explain how he managed to tame those Otherworldly Demonic puppets, Zhang Xuan had planned to have 'Yang Xuan' make an appearance to save the day.
Thus, through his mental connection with his clone, he had the latter appear in Yang Xuan's form.
Zhang Xuan had initially only intended to have Yang Xuan scare the others just a little, but who could have known that he would blow the entire matter way out of proportion?
Looking at the wreckage around him, Zhang Xuan slapped his forehead in frustration.
All his clone had needed to do was prove that he wasn't an Otherworldly Demon, but that fellow actually turned the Elder Hall, along with many other crucial buildings, into rubble…
As for how everything had happened…
The powerful aura, which his clone seemed to emanate, was from Vicious, naturally.