Debris from the road is classified as a road hazard. Doesn't matter who's vehicle "kicked it up."
If it was a part of the load that was falling off of the truck (dump gate leaking rocks or cinder), then it would be covered.
The State of California will also pay damages caused by road conditions (but not potholes) created or caused by them or their subcontractors. An example: A CALTRANS paving contractor leaves a 4" drop transition where payment surfaces have been ground down. A Porsche hits this dip, and the front airdam/spoiler hits the pavement, breaking the spoiler & fog lights. This would be a covered event.
Rocks & broken windshields are just one of the expenses of being a car owner.
Check out a windshield overlay to prevent chips & breaks. There are a few available.