During a visual approach at night you have to maintain your last assigned radar altitude until established inside the circling area or 5 miles not below the vasis.
This incident appears to have occurred at night onto runway 11 in DN,there are other requirements for an arrival onto a ILS equiped runway that allow you to descend earlier AIP 1.1-17/18 cover these (Remember this is in Controlled Airspace).Being cleared to a 5nm final does not mean you are no longer under radar control unless the controller states "Radar services terminated", how often have you been widened out in say ML after being cleared to the OM(5nm final for non locals).In this case the A/C should have been cleared to 1600ft at 18DME.
This problem occurs occasionally at other ports as well.Visual approach requirements are a bone of contention and are often miss understood by both pilots and controllers.In this case the pilot concerned is correct. As for accepting a visual approach at 30 miles,why not ,no hills, probably good wx this time of year.