I agree that this is generally good practice, and if the interviewee explained that it was just to dodge problems with making assumptions with a large codebase/

I agree that this is generally good practice, and if the interviewee explained that it was just to dodge problems with making assumptions with a large codebase/build process I would always give them extra points. It almost is telling that the codebase that the interviewer was working in was rather small (not in a negative way) that these stylistic issues didn't fit his current mental model, but such is the way of C++.