I've had to do both, but presenting on a prepared topic was much more common. I don´t recall ever being graded on a novel exercise presented to the class, but I certainly have had to solve them.
I've had professors that like to require writing on the board as well. But as in your case the key difference is, they weren't graded.
That being said, a professor student relationship isn't analogous to an employer employee relationship. Hopefully an employer wants to make the interview process as enjoyable as possible to attract as many qualified applicants as possible.
I agree, the relationship is not analogous at all. That's why I said I was going on a tangent: I was more interested in learning about the evaluation system in the US than it's possible parallels with job interviewing,
That being said, a professor student relationship isn't analogous to an employer employee relationship. Hopefully an employer wants to make the interview process as enjoyable as possible to attract as many qualified applicants as possible.