Car Club liability

Hi guys Great site you've got here! I was hoping you could help me...
Our local car club attended an event at the weekend at a well known drag strip. We have a club stand where the cars were parked together.
Whilst driving from the campsite to the clubs allocated display area, an incident took place which I was not witness to.

The scene: Car one carrying driver x, wife x and cousin x Car two carrying driver z, 3 passengers who were friends. No occupants of either car are members of the club, but were allowed to attend the event with the club. Both parties had driven to the show together and had camped together.

The incident: Cousin x got out of car one which he he was in and jumped on the bonnet of car two, causing a minor dent. Driver z did not complain at this point. Around 7 hours later, driver x left the show. Driver z realised there was a slight dent in his bonnet and called the police. A complaint was filed, details were given and witness statements are being taken.

Today, driver z's mum has phoned me as chairperson of the club to ask if the club will pay for the damage. I have said no, as we are not liable for any damage. We have helped and will continue to help with the claim against cousin x who caused the damage, but we are refusing to pay for any damage caused.
Am I right in doing this? We are not a huge club so don't have liability insurance, but I'm not sure this type of incident between 2 non club members would be covered. Any advice please? Thanks.