The aircraft wouldn't be impounded purely on the basis of the incident described. Detaining an aircraft is an extremely serious procedure and requires the airport authority to be in possession of a Mareva injunction.
As has been been intimated, it was almost certainly a case of unpaid fees being involved.
The CAA have the power to detain aircraft but they could only do so with a similar legal order (which take weeks to establish, unless previously proven) and it would involve far more serious circumstances than unpaid bills.