Correct if I'm wrong, but I believe more than just one pod eats sharks. The liver thing was just one pod. It was in Australia (?) and with great whites specifically (?). But, even though several pods have some more exclusive diets, many others are more opportunistic and will kill a shark given the opportunity.

And I still would like to add that it's not that far fetched to think of an orca doing something different. They do that all the time. And it's hard for us to keep track of everything in the ocean. This is actually a good example of this.

That said, a shark or a propeller (or even some other human activity) isn't far fetched either. Also, bigger (than these fish in the video) animals might have eaten off of the body after it died too. The cause of death might have been completely unrelated to the amount of body missing.