The regulation does not define 'extraordinary circumstances' leaving it up to national courts to interpret it.
The Regulation also does not provide for compensation payments for delays of any type. However the ECJ ruled that a delay could be as harmful as a cancellation, but left it up to national courts to interpret if and when a delay is deserving of compensation. The general interpretation is that a delay should be at least 3 hours and resulted from something under the direct control of the airline.
It would appear that in your friends case the CAA, who is the UK's National Enforcement Body, is of the view that this particular delay was due to something under the airline's control. But the CAA cannot force the airline to pay compensation- that is the remit of the courts.
I suggest your friend consult with a lawyer experienced in R261 (who will take a share) or consider small claims court. Having a CAA interpretation will certainly help the courts decide, but it isn't a guarantee.