The candidate wasn't supposed to know the questions in advance.
> The second part sounds like areal curveball
That was the point. The candidate wasn't supposed to know the questions in advance. Once the candidate can practice / memorize, there's no way to evaluate the candidate.
I had the same impression. It sounded like he was given the questions for preparation as part of the company’s process, and then OP deliberately tricked him by asking him one that wasn’t on the official list.
> The second part sounds like areal curveball
That was the point. The candidate wasn't supposed to know the questions in advance. Once the candidate can practice / memorize, there's no way to evaluate the candidate.