Janet and Colin Bord, in their ‘Atlas of Magical Britain’ explain that King Arthur killed a giant (or maybe a rival king) here. And, (also confusedly) Arthur or maybe the Giant is buried here.
If you look under a hedge nearby you might spot the ‘Quoit Stone’ which has hollows in it – these were made by the giant’s elbows. Or maybe by Arthur’s knees when he stopped for a quick prayer. Or maybe the heel marks of some people who were playing quoits.
Hope that’s cleared that up.