Most real-world scenarios aren't so arbitrary, and hardly any have a "right answer". If I had a candidate that broke out of the box of our interview to give a good answer, and that's not the answer I "want", I'd be more likely to believe the interview question is the problem, not the candidate.

remember 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. if they again say "well that is dumb i would just use sheets", that is absolutely an interviewee problem.