- When another vehicle kicks up debris off the road, the driver isn’t at fault – for example, if the truck in front of you drives over a rock and it hits your windshield, they’re not responsible for the damage.
- When another vehicle drops debris (gravel, trash, tools etc.) it’s transporting the other driver is at fault – for example, if a contractor drops a ladder off their truck they’re responsible for any damage to your car.
As a practical matter, I would bet that if your windshield is damaged by an object that could have come from either the truck or the road, you would have to prove it came from the truck, so some third-party proof (e.g. video, witness) would be necessary. So staying back is good advice, even if their "warning" that they are "not responsible" is wishing thinking.