Why did I spin a main bearing?

I have been watching and reading this thread. After looking at the pictures several times and reading the posts several times I am thinking along these lines.

1. I can't see how that peice of metal got past the screen on the pick up tube.
2. Oil Pump clearly has damage.
3. Metal was in the oil filter.
4. No obvious damage to the mains and crank bearings.
5. Squeals and noise with loss of oil pressure.
6. Engine died when this happened.

With all this I have to wonder if there was a peice of metal that stayed in the oil pump when it was manufactured or maybe there was a peice of metal inside the pick up tube? The damage to the oil pump would account for the noise and it binding up from the peice of metal could kill the car. Now guys correct my reasoning here if I am off base.