The question in the article was 'will you please tell me about the best project that you’ve ever create', which excludes most work projects, since work projects are typically not single-developers projects.
It's an interview, meaning that's real person talking to a real person. The question clearly invites to a free dialogue, it's not right/wroooong, quiz-test question. So the person answering can be slightly off topic and it can be still interesting to the interviewer, who is, as far as I can't tell, not a stubborn HR robot.
It doesn't mean you can't have created a sub-project of a larger project, if you want to get picky with semantics which doesn't seem to be the nature of the interview.