The Article speaks for itself.
I have met many Atheists that know the bible back to front and they take great pride in their research and how their knowledge (not faith) shaped their decision. Just because people don't agree with something doesn't mean they can't understand it. The very nature of being an athiest means you are constantly challenged for your beliefs, they often need to understand the bible in order to defend their stance. They also , often come from religion and decide (after alot of reflection and study) to change their status and no longer believe in a god or a religion. Many people in religions tend to have blind faith rather than study ( not all - but many that i know).
I grew up in a strict catholic family, went to a catholic school and yet my husband who was a jehovah's witness knew far more about the bible and the catholic religion than I did.
Some religions encourage studying their own beliefs as well as others, others tend to rely on the premise that their beliefs are true so no need to investigate their own religion. Atheists, often know alot about the bible but also about other religions - which puts them at an advantage in some situations. The survey showed this as well.