It mostly filters for people who spend a lot of time preparing for interviews, practicing that problem or similar ones, from books of problems known to be asked

It mostly filters for people who spend a lot of time preparing for interviews, practicing that problem or similar ones, from books of problems known to be asked by interviewers. In a more general sense it filters for people who want a job badly enough to do the goofy dance that many companies expect of candidates, and are savvy enough to know the dance exists.