...was informed no ranking existed....
This is not unusual. Of course there is an internal ranking based on performance in the sense that a minimum standard is set and you will need to score over that level to be offered a place. "with no minimum pass mark" might suggest a certain amount of subjective marking where one area shows potential but currently is somewhat lacking.
I think what they are eluding to is that no full ranking is ever made. i.e. The candidates will never know how they compare to each other.
I think this is a good thing... it means they start school on an even footing rather than peer comparison on the basis of one day's exam results, some of which may have been heavily prepared for.