As an interviewer, it's my role to get the information I need to help inform a decision that I will not make alone. If I have a concern about some unknown, I have to navigate that; it's on me. I expect an interviewee to be prepared to share relevant information, but interviews are stressful and if I only want to hire good interviewers, I'm going to have a considerably smaller pool.

Furthermore, as an interviewer, my job is to be a candidate. Why should this person choose my team/company to work at? It's a privilege that anyone show up to join, and I ought to be as prepared to give answers as they are.

That said, any "feedback" I would give would be arbitrary. I am not this person's mentor and I shouldn't—after only 40 minutes—assume I know enough to give them feedback. Saying that I have concerns about not getting enough information, and that somehow being their "feedback," is bad framing. Try:

  Before moving on, I really want to make sure I get a full picture of your time at Acme working with the Foobar team. Would you say that you led project X? Who ultimately decided when it shipped and set deadlines? Was that part of your responsibilities?

I know TFA mentioned similar things about also being a candidate and that the "feedback" is to spur discussion, but the framing of giving "highly opinionated" thoughts about someone's capabilities as a way to ask questions is unnecessarily adversarial is an already power-imbalanced situation. I think it's better to try to tilt the power imbalance in the other direction—giving the candidate a feeling that you, the interviewer, are also auditioning for them. Doing that shows humility and, in my experience, gives a better opportunity to get to honest answers about being a good fit for each other.