i don't think you would even be liable if you were driving your car coz it happened on a private car park. I remember this happened to my brother when he had a collision years ago, he couldn't claim off the other driver.
what makes you think it came from your wheel? I just cant see that riding at a normal speed would do this, would the stone even get the required lift? seriously, are you sure someone didn't try to shoot you with a pellet gun, and hit the car instead, and you just presumed your bike kicked up a stone?