Because it is that Stephen Jay Gould's principle of nonoverlapping magisteria considers the existence of God to be a scientific hypothesis like any other, not Richard Dawkins thinks so.
Context:
Dawkins is an outspoken atheist[66] and a supporter of various atheist, secular, and humanistic organisations.[13][67][68][69][70][71][72] Although he was confirmed into the Church of England at the age of thirteen, he started to lose his religious faith when he discovered Darwin.[73] He revealed that his understanding of evolution led him to atheism[74] and is puzzled by belief in God among individuals who are sophisticated in science.[75] He disagrees with Stephen Jay Gould's principle of nonoverlapping magisteria[76]
and considers the existence of God to be a scientific hypothesis like any other.[9]:50
More:
https://en.wikipedia.org/wiki/Richard_Dawkins#Advocacy_of_atheism