Yet, that idea fades as multi cultural influences are introduced.
So an American atheist is sociologically inhabiting a Christian country. But it is interesting that we hear of CINOs, Christians in name only, (the ones often cited as a source for what non believers think Christians are), but not atheists in name only.
There are Muslim countries that by law do not allow other religions, so they are often uninfluenced by other religious beliefs.
Their countries are authentically recognized as being Muslim.
I suspect Dawkins is just acknowledging that he subscribes to the moral/legal foundations of our country.