The 'atheist' in the study is not a person, but a straw man. This is due in a large part to the fact that religious individuals poison the well against members of other tribes, both to create new adherents and to prevent adherents from becoming apostates.

You seem to be falling victim to this by assuming that a persons belief in the existence of a supernatural special pleading changes whether they subscribe to a personal moral code, and that some moral codes are more or less moral.

By your comments it's clear you missed the point of the study, or at least the poorly framed article, which is to point out that this kind of thinking is in fact wrong. Adding an extra point of irrelevant data, in this case a persons belief or non belief in deities, doesn't make it more or less likely to be true or accurate.