Casting lots for clothes

John 19
It seemed amazing to me that David would foretell about the casting of lots for Jesus' clothing.  John 19:24 includes a reference to Psalm 22:18, in which David says that he has been surrounded and attacked and his clothes were divided among his enemies, by casting lots.  This passage in Psalm 22 doesn't really seem to speak to future events, but rather describes what was happening to David when he had written this particular psalm.  Why then does John include this passage as a "fulfilment of scripture"?  It seems more like a nifty little similarity rather than a fulfilment of a foretold action.