My biggest criticism of the task is that the article doesn't make the goals of the task - i.e. what the signals are that they're looking for - clear at the start. You can see in the comments that a lot of people have gone in looking for a kind of trick and made the whole thing more complicated than it needs to be.

I can imagine in the real interview, there'd be more build up to the task, and a description of what the interviewer was actually looking for. That way the interviewee understands what the purpose of the exercise is and doesn't end up lost down rabbit holes.

The more I think about this idea, the more it grows on me though, if you frame it well and find a task that can be explored in the given time frame.