It might be how they would explicitly define a code of morals, but I think they just don't understand why they have morality. When I was still a theist, I wondered why there'd be any reason for an atheist to have morals without the promise of heaven and the threat of hell. I suspect lots of theists ask that. I didn't base my every action on greed for heaven and fear of hell and I doubt many theists do.

Is it? My impression is that most people would consider utilitarianism to be a moral code, even if they thought it a terrible one.