Roland was clear that it was nothing but his own speculation.
I can't jump to a conclusion based solely on the documentation of the underground civilization since their contents still need further verification. For example, the underground civilization thought that they successfully survived a series of competition, but what about their opponents who probably were also able to use magic power? Where did they leave their traces? What about human beings? Did witches first appear before the first Battle of Divine Will— or rather, was the mankind gifted with the sense of magic when they were still primates or even at the beginning of the Mammalian age?
Maybe, human beings in this world didn't go through such a long process of evolution at all. Could they directly become what they are now through mutation after gaining a victory?
He was afraid that to answer these questions, he would need a great number of outstanding explorers like Thunder.