I use to handle insurance claims, so I do have a little back ground on this sort of stuff. Whenever a person is legally liable to someone else, either for bodily injury or personal damage, you would have to be negligent in some way. In other words, you have to owe some duty to someone and you have to have broken it.
By simply riding your bike and a rock was kicked up does not mean you are negligent. What did you do wrong? Nothing. Now, let’s look at this like the Myth Busters, what would you have had to do to be negligent. Say every morning you ride real close to the dude’s parked car. And every day, the owner of the car tell you, hey, you really ride very close to my car, and I really wish you would not because some day you’re going to hit it, or kick a rock up or something. Well, at that point you are put on notice, you are now aware of the situation. So, you say, screw it, I'm riding the way I always have, and now you damage the car as you where riding real close, now you might be liable.
So getting back to his case, if the owner of the car made a person liability claim against you, I (we) would have denied payment on your behave to the owner of the car. (Your Homeowners insurance policy provides personal liability coverage) And we would have defended you, if need be, as you did nothing that a reasonable and prudent person would have done in the same situation.