Sorry to be the only dissenting voice, but I think the answer is “it depends”.
Some strata insurance policies (e.g. your sponsor’s) cover “proprietors fittings and fixtures” in addition to common property.
So, in general terms, just because there is a claim on the strata insurance policy, doesn’t always mean it’s the OC’s responsibilty and cost (excess).
In this case, because the splashback was an original hard surface attachment to a common property wall, I think it is the OC’s responsibility, but not necessarily cost.
Some strata schemes (e.g. ours) have a By-Law concerning common property which amounts to “you break it, you pay for it”.
So the question arises, how did the splashback break?
Was there a minor earthquake which stressed it to break?
Or did the cook accidentally hit with a heavy-base saucepan?
If of the latter nature, why shouldn’t the Lot Owner pay the excess and just be grateful that the OC’s insurance has covered the majority of the cost?