I understand that I just don't consider it cheating despite their reaction during the interview. I'm not going by any formal definition of "cheating" here. But

I understand that I just don't consider it cheating despite their reaction during the interview. I'm not going by any formal definition of "cheating" here. But this person took the question as a practice question, not with the knowledge that it will be asked. They also did the work on proving and understanding it. Let's put it another way. If you take an exam after practicing with any kind of practice questions (something that has been done since the dawn of time and the education system) and happen to run into the same questions in the real exam, was that cheating or better targeted learning? Or if you find out about a job from a friend who works there, is it cheating because you have a significant insider advantage over people who never knew about the job? In my opinion true cheating would have been made up of a) someone feeding them the real questions and/or b) someone feeding them the answers. It involves an unwillingness to put in effort and a premeditation that I didn't see in the story. This person was indeed in a conflict of interest but I wouldn't call them "a cheater". P.S. If I were in that interview I would have provided the full answer almost instantly, not needing any kind of hesitation to "simulate" the thinking process. I know the answer without any relation to the interview. So there could be 2 outcomes: a) I get unfairly excluded under the suspicion of cheating justifying the need to fake the thinking to avoid this or b) I would have passed to the next stage making that whole charade effectively inconsequential.