Global One
A rather unlikely event. A power plant would not be striking the vertical stab, not even the horizontal after a separation. Looking at the picture, it does seem to be a clear "cut", as Ranger One has mentioned, "un-riveted" almost. I can't come up with any plausible scenario causing such a separation myself either. In any case the vertical stab being separated in such way, found in bay can't have anything to do with a possible uncontained blade separation.