Wondered that myself then settled with - I'd guess it probably developed naturally as satellites would have exposed Chinese dredging and construction activity as seen in other places. The added interest here i think is more because it's yet another one and strategically located with the other three mentioned. These appear key:
"Outspoken Foreign Secretary Teddy Locsin Jr on Wednesday asserted that Whitsun Reef was “not an island; should not be made one by reclamation in legally ludicrous attempt to turn it into one generatingan EZZ that swallows Palawan (a large island that forms part of mainland Philippines)”."
and
STRATEGIC CHOKEPOINT
Whitsun Reef (Julian Felipe Reef to the Philippines and Niu’e Jiao to China) is a shallow coral reef that is usually only exposed at low tide. But in recent years, a 100-metre long dune has grown as a permanent presence.
But its position makes it something of an international crossroads.
“As the easternmost feature in the Spratlys’ multi-nationally occupied Union Banks, it is strategically situated astride busy sea lanes — an ideal base for monitoring and operational dispatch,” says Professor Erickson.
Whitsun Reef sits at the centre of a triangle of China’s Spratly Islands fortresses, formed by Fiery Cross, Subi and Mischief Reefs.