Sometimes when I read atheistic writings or publications it seems like the term "Christian" or "Theist" is taken to be interchangeable with "Creationism". I think this shows a fundamental misunderstanding of what it means to be either a Christian or a theist, and it also shows a lack of understanding or awareness that there are different forms of creationism.
There is Young-Earth Creationism, which holds that the Earth is only 6000 years old, there is no evolution, etc. There is also Old-Earth Creationism, which holds that the six "days" in Genesis were not literal 24 hour periods, God may have used evolution as the mechanism by which He created man, etc.
Here is a handy little graphic I found that illustrates each view.