I would assume it means anyone needs to show proof of vaccination, local or not But it looks like to me there is a difference between someone going by sea or air from Sint Maarten to St. Barts. For travel by sea, so long as you're vaccinated, you're good to go. But if you're travelling by air, then you need a compelling reason, which one would have to assume would NOT include a pleasure day trip. Why a difference between sea and air travel doesn't make sense to me. But, if you're travelling from St. Martin, all you need is vaccination, regardless of whether you travel by sea or air.