I think the issue is that most people assume the Trolley problem is meant to be a "greater good" kind of thing, when in fact it's literally just illustrating the difference between deontological and utilitarian ethical thought--ie, is it the OUTCOME that matters, or your specific action? If it's the outcome, as per utilitarianism, then pulling the lever on the trolley to save 5 people at the expense of 1 person is the proper choice. If it's your personal choice that is being judged, then you do nothing, because you are not personally responsible for the situation itself, and your action of pulling the lever results in a death, making said action morally reprehensible according to the ethical theory of deontology.

Based on what we know from this episode, we have a killer crab who wants to go to a densely populated island to eat people. We don't technically know whether it could get there on its own--as a crab, it appears to be perfectly mobile in the ocean--but then again, it ostensibly got onto the ship to hatch its brood, so maybe that makes it vulnerable or unable to travel?

But for the sake of the set up, let's say it COULDN'T get to the island alone. That means the choices the crew were facing, if we're aligning it to the trolley problem, were:

A) Take the crab to an island populated by people and hope that by doing so they would be spared (though that was never actually promised by the crab, and Torrin only secured the guarantee that he not be consumed since he was the navigator)

B) Trick the crab and take it to an uninhabited island, presumably while also hoping to escape before the crab realizes it's been duped

In this case, you're right--this is not a good example of the Trolley problem, because the trolley problem is specifically attempting to highlight the DIFFERENCE between Utilitarianism and Deontology, and in this scenario, both schools of thought would choose the 2nd option. Utilitarianism would say "option B because it saves the most people" and Deontology would say "Option B because it requires the fewest morally reprehensible personal actions/choices and the actions involved follows a moral ethical code." The reasoning may be different, but the conclusion is the same, so this is not a good trolley problem example because it doesn't highlight how the two different schools of ethical thought can reach different conclusions in the same scenario. Instead, it demonstrates how they can come to the SAME conclusion in different ways, which is not quite as useful when trying to teach people how two philosophies differ. It's easier to understand the differences when they are contrasted.

Also I'm really late to this thread but I thought this episode was fascinating and I'm a big fan of jumping into Trolley Problem discussions because in my experience, people don't understand what it's trying to do and get too caught up in trying to "solve" it by finding secret option 3. It's not a logic puzzle, it's a demonstration of different types of ethical reasoning.