This whole snipe hunt you've led us on has been off-topic.
Off the top of my head, acknowledging that babies and rocks are atheists refutes the claim that they're Muslim, which I've heard some Muslims make.
Yes: originally, it meant someone who didn't believe in the mainstream god(s) of that particular society: to the Romans, Christians were "atheists" because they didn't believe in the Roman pantheon.
In more modern European history (i.e. the last thousand years or so), "atheist" generally meant "non-Christian", and since baptism was the rite of initiation into the Christian religion, a newborn, unbaptized baby would have been an atheist.
What you are and what you identify as are two separate things. They don't necessarily have to be the same.