Hi, Graham. No, I don't mean to be saying that at all. Theists and atheists have different troubles accounting for morality.
Theists appeal to God's commandments, but then there's the Euthyphro dilemma. Why is it moral to obey the most powerful person's commandments? Isn't that just slavery?
And atheists face the problem that morality looks to be arbitrary in its subjectivity, given the alien, inhuman character of natural reality.
In any case, whether atheists are more moral than theists is a sociological question, not really a philosophical one.