For these people science explains how the world was created yet religion explains why it was. Even today there are disagreements among scientists about how and why the 'big-bang' occurred. For example, in Genesis 1 it says that after God created light on the first day there was evening and morning. Yet later on in the chapter it says that God later created the sun, moon and stars on day four. The fact that some people believe science and religion have different views on the origins of the world does not necessarily mean there is no God.
Atheism is a rather extreme position to take with regard to religious belief.
In the light of this some people might say they do not really believe in God yet at the same time not want to rule out the possibility that a God might exist. Such people are known as agnostics .