this is all based on literature found in TES no? by this logic, i could say everything in the Bible is true (which most people in Europe DID used to believe)
TES isn't Earth, and its literature is all we have. When all literature says the same thing its pretty safe to believe that its true.
[edit] And people have been around since the beginning of time. All mortals are just the descendants of gods, and all creation myths are just somewhat distorted histories.