No, I don't think it's semantic. This basic distinction between life and nonlife cuts to the core of it, I think. We know basically what life is, even if we can't explain every facet of organic processes. And thanks to the scientific overturning of Aristotelian teleology, we know, superficially at least, what nonlife is: nonlife is physicality that lacks mental guidance. But we're much more familiar with life than nonlife because of our internal perspective on ourselves. We lack that intuitive grasp of nonlife, so acquiring some such intuitive familiarity is the atheist's positive challenge.