When I said, "An atheist is one who does not accept the theistic claim," I assumed that "one" would be understood in the context of this statement as implying personhood or at least sentience. It seems that some people are now trying to pretend that inanimate objects would count as atheists. Maybe that's not a big deal. If rocks are atheists then there are a hell of a lot more atheists than religious believers!
But seriously, when dealing with such concrete thinkers, maybe it would be best to phrase the definition as follows:
An atheist is a person who does not accept the theistic belief claim.Perhaps that will be clearer.