The rules of reporting weather via metars at aerodromes in the UK changed on Oct 6th this year.
In my opionion the reported metar should have been reported as CAVOK but I'm guessing the new rules have confused the met observers at GP as much as they have us at KK.
The new rules basically mean that cloud above 5000' is no longer reported in a metar. There are other changes too including reporting of RVR's greater than 1500m.