That's how release clauses work, at least in Spain. Officially speaking, the player has to buy out his contract, so that he is free to sign for a new club.Sky sports news have the yellow ticker tape with the following headline..
"Athletic Bilbao say aymeric laporte has paid buyout clause in his contract.."
If you read that you'd say the player has bought himself out wouldn't you?
Just think the wording of that statement is a bit strange.