Evidently you have little experience with hyperbole.
It is the rhetorical use of exaggeration for effect.
Your argument would make him anti-science because he is anti-religion.
This makes no logical sense.
Hitchens said that "mockery of religion is one of the most essential things." Is now a bad time to mock Collins's religion? Perhaps, according to the atheist way of handling things, it is best to mock someone's religion when you don't need their help, or when their back is turned.
It is the rhetorical use of exaggeration for effect.
Or, to go a bit further, his present relationship with Collins is a way to say that everything he previously said about Christians was a load of lies and slander.