It is also an acceptance of a moral code - for example, the 10 Commandments. If someone accepts this code they are less likely to murder and do other 'forbidden' things. Of course, one's system can be more 'moral' (e.g. Islam), or can be less (e.g. 12 Step paganism). But at least it's a known quantity. Not so for the atheist. Of course, the avowed atheist typically has given thought to morality. But the 'atheist' in the study probably just means someone who hasn't given the issue much attention in their life and I for one would be more cautious about such people.