I think more details are needed.
It seems to me to be a plumbing leak investigation done by the OC which turned out to be caused by a lot owner? In those cases, an OC often tries to recover its costs.
I’m guessing that the OP themselves reported the leak to the OC or called the OC’s emergency after hours service? Sometimes OCs or Strata Managers have a policy that if a reported issue turns out not to be a common property matter they will recover the costs from the requesting lot. IME, it’s SMs that drive this policy more than the OC itself or the committee although it can be approved at each AGM.
It really should be that they recover the costs from the responsible lot. I’d agree that the committee should be contacted, especially if it was another lot that was found to be the eventual cause of the leak.
As for the insurance, some policies do cover exploratory costs. With a fair few conditions attached. You could check directly with the OC’s broker or the insurer. It’s the party who eventually has to pay for the exploratory costs – OC or lot owner – that makes a claim.