It almost appears as the spoiler had been fully deployed when it was torn away. When stowed, it's a fairly firmly rooted panel, and flush to the airflow across the wing. I'm trying to visualize the type of odd flow that would pull it out of the wing while stowed. Looking at the hinged corner failures, it would appear the spoiler failed forward, away from its mount, with the airflow from the trailing edge of the wing flowing forward.