Literally he’s saying to behave inappropriately in a professional interview and see if the candidate plays along. Might as well see if you can get the candidate to offer a bribe or sexual favors for the job since we’re going all in on entrapment.
Of course it depends for what field and role you apply. For any leading role or customer contact point the capability to stay professional is essential. If you flip burgers at McDonald's then it's your right to be grumpy.
This is unethical and it’s also a shitty filter because they people you want to hire (the ones why won’t talk personal stuff at work; or won’t drink on the job) are likely to write you off because they also don’t want to work with the guy who wants to drink margaritas and chat personal trauma at work.
This is a leading role(!) in the mental health(!!) industry. That should give some clues. They also announced that the follow-up interview as a "non traditional - a ~90 minute culture fit chat" dropping more hints.
Unfortunately he also "fail to recall the exact wording of the discussion topics".
I bet the exact wording was open enough to leave enough room to not "felt completely emotionally drained" afterwards.
I think the interviewer did him a favor. He is just not able to handle a leading role in the mental health industry in a way that would have been mental healthy for him.