At least in my experience the main difference between exams and interviews comes down to relevance. That is, an exam will be within the context of material you'

At least in my experience the main difference between exams and interviews comes down to relevance. That is, an exam will be within the context of material you've been studying and an interview just... kinda whatever? I have only very, very rarely seen -- from both sides of the table -- professional interviews that are associated with the job the person might do. This problem is worse the larger the company, once there's a standardized set of questions to evaluate someone's possible fitness for a variety of roles. When I've had power over the interviewing process it's always been enlightening to ask the interviewer to take their own interview. I'd be willing to bet most professors can pass their own exams; the same hasn't been true of interviewers.