Are the rod thread bolts stripped? It appears maybe the bolt backed out just enough and the crank slammed the rod down or up and at that point pulled the bolt out and brought half the rod with it. I would think it would pull the rod bolt out, stripping the threads along the way, versus breaking the rod in half. :shrug:
Edit: I guess angle and thrust can do anything while at high RPM in motion. None the less, sorry for this happening to you, but thanks for sharing.