We would have to know that there wasn't a god before we could tell.
Just because someone doesn't believe in a god doesn't mean that there isn't a god. One who still guides their thoughts and actions, until such time as they realise that there is a god. Or never realise.
Silly question.
For the record, I still had excellent morals when I was an atheist. Better than many Xians which is probably why, although I now know God exists I'm still nowhere near being a Xian. But then again, as I know God exists I have no need for a belief system.
