Based on my personal experience of automated testing in AAA games, even if you "only" count the overlap with the actions humans take, it's a huge overlap in practice. And while there are edge cases only humans find, automated testing finds bugs humans don't.
The point of that section is that the earlier you find bugs, the quicker you fix them, and you end up with less overall pain for the length of the project.
The point of that section is that the earlier you find bugs, the quicker you fix them, and you end up with less overall pain for the length of the project.