There are lots and lots of people in here who have never owned a business or had to hire someone. Case in point, the candidate badly answering an obvious question saved the OP the trouble of wasting more time on the interview.
I posted an administrative assistant position and got hundreds of responses. When you get that many people, you have to be picky. It amuses me slightly that most of you who think the question is THAT stupid are probably bad employees, or at least somewhat lazy and entitled. That type of mentality is exactly the type that fails the annoying questions such as the one posed in the OP. No interview is perfect and people are often good at lying, but if you can catch some of them when a silly question, why not? From my POV, it saves me time and money to have you fall flat on your face during the interview instead of 3 months later.
Hiring someone costs a significant amount of time, money, and energy. Hiring someone who can't separate their personal and mostly unjustified feelings about a simple question usually ends badly for the company. When I've been asked questions that sounded pointless, I gave a clear and concise answer so we could move on to the meat of the interview. Not having that skill or thinking you're too good for the question is telling.