Guessing that Vishi is the Ghost Prophet is hardly difficult.
Or rather, he never intended to hide himself.
A strange Holy Sanctuary Mage, not only well-versed in divine secrets but also possessing the Miracle to directly dominate the souls of Legendary Mages, acts in a bizarre and cruel manner. With so many factors combined, and given that even a dog would know the Ghost Prophet just revived in the Distant Realm last month, it would be odd if Ash and Weiser couldn't guess that Vishi was the Ghost Prophet.
