anType, Id think its a Brunei Plate, Kuala Belait/Seria area to be specific. 2 reasons:
1) Miri, Brunei vehicles are common. Kedah Plates.. not much if any. So to spot a K* plate in Miri, its 99% Bruneian car.
2) Thats a typical Brunei font/type plate. They cant use any others..
I was born in Miri.. lived both places :) No arguement intended. But if you wanted to be sure, Im sure the car can be spotted again in Miri. Not hard to find ;) When its appears, take a picture to see if it has the Malaysian roadtax