It is quite simple.
A Public Liability is a policy of provable negligence. As an underwriter of many game and clay shoots this is something I would expect to pick up and pay as a legitimate claim.
Risk assessments should have been carried out beforehand and, unless there was something like freak wind conditions on the day, they were clearly inadequate or not completed.
Disclaimers mean "diddly squat" (not an insurance term). We tend to insist on them but know they will not stand up in court if seriously challenged.
If that was my car I would be sending a letter with repair estimates to the shooting ground and asking them to forward it to their insurers.