Humans… of course it was always humans, it cannot be any one else but them. A place that's supposed to be secret that no one had any idea about… allegedly anyways. And the day it opens they find humans waiting there already for the entrance to the mystic realm to open.
This was another reason for Divyat to doubt Zhurong, especially when you consider the fact that he could feel powerhouses of the nascent soul realm amongst the people on the island. This was not a fight that they would be able to win, even with his new found prowess. The nascent soul realm was a breaking point, every other realm up unto the nascent soul realm would be considered the training realms.