A mystery

The Weston Favell churchyard in Northampton says that it is a Commonwealth war graves site.

There is only one such grave and this is it.

Derek Skey was a Flying Officer in the Royal Air Force Volunteer Corps. He died aged just 20 towards the end of World War II.

But how did he die? The records I turned up said that he was one of only 3% of airmen who died with no recorded cause of death;

The records further show that his parents, who were buried with him much later. were both from Northampton. So why is it a Commonwealth war grave? Is it simply that British people are also members of the Commonwealth?