I did many "interviews" as a casting agent for films, so finding the suitable actors for one or more roles in limited time.
Thank you for highlighting the randomness, because I can't understand the (what must be fake) confidence of some interviewers in their assessments. They think someone who aced the interview will be good in their role at work. How often I had to work with what can only be described as sly, but lazy con-men that "really interviewed well", but couldn't even do the most basic tasks, says otherwise. Unless their role is doing interviews all you get from an interview requires some degree of extrapolation towards the real job. Additionally people may have different days, different characters that make them shine or suck at doing interviews and maybe that specific task was just a mismatch and another one would have made them shine.
Interviewers that are not aware of this have not reflected what it means to do their own job in my opinion.
This is why I also try to make the interviewees shine by giving them the best cards possible. To some degree that mitigates the randomness and it also helps soothe overly anxious or excited candidates. They should get the feeling that I as the interviewer try to solve the posed problems together with them, not that I throw bricks their way and try to misunderstand everything they say. I also try to make the tasks in the interview emulate what needs to be done in the actual job/role. Everything else would be silly.
I have actually gotten great feedback on that way of doing interviews over the years.