The generic definition doesn't even need to move, as words are far more flexible than that anyway.
People get too tied up with dictionary definitions at the expense of usages, as if words lead monadic existences isolated from any broader context. Usage may be figurative or contextual, for example you could contrast the atheism of Dawkins with that of Nietzsche.
Here you are going beyond the dictionary definition and including the aspects of their worldviews that are built around attitudes towards god and religion, but it makes perfect sense in context. Unfortunately, you'll still get some pedant who likes to pretend they can't understand this as it doesn't conform with dictionary literalism, like those who pretend they have absolutely no idea what New Atheism is simply because it's not literally a new form of atheism.