alt Hacker Newsremember that we already did the "Excellent answer, that is what I would do as well, now what if we wanted to build it in-house?" part.
the "good answer" was already acknowledged, the "real-world scenario" answer was accepted.
the second part ("what if we wanted to build it in-house") is purely hypothetical to gauge how the interviewee would approach the specific technical challenge (shedding some of the "real-world" constraints so that the focus is technical).
if they again say "well that is dumb i would just use sheets", that is absolutely an interviewee problem.
Depends on the dyanmic. If you have an excellent candidate you're trying to poach, it becomes an intervewing problem because you're wasting both you and their time.
If they are a dime a dozen, then it becomes their problem. Whether or not they care it's their problem depends on their circumstance.