Wouldn't suprise me if he'd puked the skull back up. Usually that's the part of whole large fish they can't digest very easily, and thus you get to see it again while your scooping it off the bottom of the tank.
your rtc doesnt see the other fish in your tank as a threat to his food source , i guess he saw that hybrid as a total threat to his food and took care of the problem!!! we learn most from our own mistakes.but its best to learn from others mistakes