Can anyone explain it to me why this submission has been flagged? Yes, I saw it some weeks ago, but if that's the reason, it should be marked as dupe, not just

Can anyone explain it to me why this submission has been flagged? Yes, I saw it some weeks ago, but if that's the reason, it should be marked as dupe, not just flagged. It is a genuinely useful website and I don't see much criticism in the comment - apart from the fact that 20 minutes for interchange is too little. Nothing that deserves flagging though.