None of these situations are the same as an interview. If you're providing an explanation at the behest of the interviewer, why not also depart on a tangent, also at the behest of the interviewer?
The role whose function an interview most resembles is that of a sales person. Having been in hundreds of sales meetings, I can say with total conviction that the ability to direct the conversation and deflect tangential questions is absolutely critical to being successful.
That said, every role doesn't require that skill, but OP specifically said that it's only for more senior/customer-facing positions.