Hello. In the UK companies or individuals providing a service or product are usually obliged to have public liability insurance, to cover costs and compensation in the event of someone being injured as a result of using their product or service. If for example a kid at a summer camp was injured because a piece of equipment, like a swing or whatever, broke, or as the result of negligence wandered off and got lost and injured - anything like that - then the organisers of the camp could be held liable to pay compensation and possibly a fine. As Jerry said, this would be decided in court, i.e whether or not the organisation could be proved not to have taken the necessary steps to prevent such an accident occurring. Here liable has the same sense as responsible, or culpable, as in to be found responsible for the incident or culpable for the injury suffered.
The humour here is in talking about the gods of Olympus as if they are just any other organisation and have to comply with the law, rather than a bunch of capricious overlords who do whatever they want.