I see these types of questions as the sign of an inexperienced interviewer. Given how many inexperienced interviewers one can see interviewing at tech companies, I would call that a chartreuse flag at best due to lack of signal.
Yup - that's all it is. And you're going to have a certain envelope of negatives (usually far worse than this) in any environment.
So while it does make the flag a bit bless verdant... to call it a "red flag" seems to be a bit of a stretch.
(And as for the substance: agreed, and a capable interviewee should know how to work around those questions and similarly silly ones, like "what's your greatest weakness?". It's a two-way street. And while it's not a positive datapoint, it's hardly a KO-criterion. (viridescent? aquamarine? turquoise? :) )