Which country’s territory is the “Wu Jiao Island” in the South China Sea next to Malaysia on Google Earth? Why is it marked as Chinese territory?

It is an hour's boat ride from Kota Kinabalu, the capital of Sabah, Malaysia. The travel agency claims it is a private island. There is a pier on the island and more than a dozen houses have been built. The cost for a one-day trip is about 800 per person, and the two-day trip is about 1,400. The locals call it Huantan Island. It has only been developed recently and very few people go there.