Never heard that, I think you are mistaking the SOURCE of morality in each group.
If i don't steal because I am afraid to violate the ten commandments or if I don't steal because I genuinely don't want to cause harm to someone else, it doesn't matter what you believe, the second reason is more intrinsic morality and not extrinsic.
there are good and bad christians
there are good and bad atheists
In either group if someone is doing good for the right reason what difference does it make what they believe???
I just feel you post this crap to instigate, but whatever here I am contributing to this nonsense.
It always comes back to this, religion is dangerous and capable of twisting morals:
“Those who can make you believe absurdities, can make you commit atrocities.”
― Voltaire, Questions sur les Miracles à M. Claparede, Professeur de Théologie à Genève, par un Proposant: Ou Extrait de Diverses Lettres de M. de Voltaire