Accountants don't create something out of nothing. It's an inherently supporting activity.
Also, the question doesn't imply in any way that it has to be an off-work project. Its only point is to see if a person actually cared for any code they wrote in the past or if they treated coding just as means to an end.
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.
Also, the question doesn't imply in any way that it has to be an off-work project. Its only point is to see if a person actually cared for any code they wrote in the past or if they treated coding just as means to an end.