I think it tries to match you with someone closer to your level first so it looks for that
And then after a minute if it can't find someone you could reasonably fight it'll just throw you anyone else who is in matching similar to arena
But if no one else is matching you're just stuck
Last time I got in I joined late and was matching for over an hour lol

I wouldn't call it a typo or a bug, it's just not really the clearest explanation