Eg, "I wanted to talk about Gmail (I used it daily) but the interviewer didn’t want to. Instead, we opted to talk about Google Docs. Unfortunately, the interviewer had been the Google Docs PM, and I’d only used it at a surface level. Every suggestion I made turned out to already be in the Product. Whoops."
To me, this has the smell of the "know it all" interviewer who is more interested in proving their superiority over the candidate than actually conducting a decent interview. Of course the interviewer wanted to stick to discussing the product they were the PM on, how else would they be able to smugly call out the interviewee on their (perfectly reasonable) suggestions?