It's an odd phrase. Are you sure it wasn't said or written as ' He's all alone '?
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dave_anonAt the moment that he takes the shot, he's totally composed within himself; he is completely focussed on what he has to do; there are no other thoughts in his mind; he's all oneFor what it's worth, that's how I read it, too.
CliveHe does it all in a single motion.To me, the rest of the sentence implies that he didn't do it in single motion. He took an initial touch, then settled, then shot.