Cadets are mainly those from the flightschool in Qatar. As well some where parents or family work in Qatar Airways. Why they interview them is a mystery and seems just the result of an incompetent recruitment. For those that turn down any offer while waiting for Qatar be very careful. Most of SO will never be called and you'll just loose your chance to find a job ! The Same goes for FO recruitment, don't wait for Qatar. Also be careful when you resign. You might end up without a job in Qatar+resigned from your previous operator!
About those that have been interviewed in 2012, most of them belong in the above categories. Be aware that some did around a year to complete the whole training.