Why do people think that the story about the sword and the stone is a welsh story?

There is some confusion about which sWord was actually in the Stone. In some versions, Excalibur is the only sWord in the story and the name Excalibur comes from the Welsh Caledfwlch. However, other stories have Arthur being given Excalibur by the Lady of the Lake some time after he began his reign (after he breaks the SWord in the Stone while fighting Lancelot).

Arthur is a legend with many sources: Welsh, Irish, British and Norman.