According to the sculptor's explanation, one would have to say that Goliath's death has to be attributed to David's wit and skill at using his slingshot.
But does the account at 1 Samuel 17 suggest otherwise?
Wit and skill goes a long way in the business of slaying dragons. It doesn't hurt if you're perceived as the Good Guy either. :) The Bible leads the reader to believe God was behind the killing of Goliath, thus teaching others a lesson, too. Of course one can argue that God directed David to do what he did, perhaps even guiding the stone that killed Goliath. It's an arguement that can't be proved because there was nothing supernatural about the event.
Looking at the recorded event (holy books are not the best record of history) the sculptor's explanation holds up to what really happened. The Bible's account lacks hard evidence. That doesn't mean 1 Samuel is wrong--there's just no proof.
If I was God, and I wanted to prove I was behind David's effort to kill Goliath, I would have done it differently. On a clear day I would have David (or better yet, a little boy or girl) go out to meet Goliath, point a finger at Goliath with a lightening bolt going from the finger to Goliath's head. That would have been proof that God was behind the event. You really wouldn't want to mess with me if I was God!