Is there any other kind of cheating?
The ostensible reason to be against cheating is that it devalues the degrees the university gives out if it can't be trusted that a person earned said degree through merit. I'm saying that a person who found the exam and learned from that material isn't going against this reason to be against cheating; they did, in fact, pass the exam on their own merit. At least, I don't see why I should consider it differently.
In this case, they cannot even appeal to that perennial cheater's excuse: "what matters is being able to get the right answer, not how I got it." Here, they demonstrated utter incompetence at that task! Their knowledge was so impoverished that they could not even identify blatant errors.
Although it's very funny that this happened on an ethics course, the "is it ethical to cheat on an exam if you learned the material" question doesn't even apply here imo
I don't see this so clearly. It seems to me that this is assumed. Why do you think it is so clear that this is what the students did?