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lunch ...
with someone who doesn't have inputI think part of this could be that they don't know whether to believe that you truly have no input.
When I was an interviewee, my lunch escort told me they didn't, and I was pretty sure it wasn't a devious trick to get me to let my guard down, but I had no way of knowing for sure. I also thought, if there isn't a formal process, maybe if I say something too dumb or wrong, they would still mention it to someone. So I stuck to really superficial topics.
Then I got hired and later served as a lunch escort. Now knowing the process and knowing there truly is no input, I tried to convince the interviewee, and he didn't seem to believe me just like I didn't when I was in his shoes.