So here is the reasoning:
If the only reason people believe in a God is because of religious texts written by men, and stories told by men, that say there is a God.
And these same religious texts deny that evolution occurred.
Yet we have evidence in our possession that the processes that make up evolution, such as cell mutation, bacteria evolution etc can occur.
Then the only reasonable conclusion are that the religious texts are wrong, and are in fact fabricated by men.