This is a mystery. The burial record says he was a soldier and the DC may say the same, but still not adequate evidence to show embodied service, unless cause of death indicates such. It's strange to see no NoK on the Effects, so no Dependent pension.
He appears to be buried in a common grave, so no family connection found.
A man born in 1887/88 and called up in 1921 must have served 1914-18...