Whitesun Reef is almost 300mi from the waters of the Philippines, you can look on a map for yourself
You should check your map more carefully. The nearest major landmass is Palawan, which the article correctly states is 320 km away. Palawan has 900,000 inhabitants and is in the Philippines. EEZs are 200 nautical miles, which is approximately 370 km, so unless the Spratly Islands are used to define EEZs then this reef is comfortably within the Filipino one.