The truck driver probably never knew it. This kind of stuff happens pretty often around the bigger areas, such as Houston, with scrap iron haulers.
Ya, I love all the gravel haulers in the Houston area who drive like total meatheads, and don't brush any of the loose gravel off their tailgates. Oh, but they are protected by the "NOT RESPONSIBLE FOR DAMAGED WINDSHIELDS" banners they hang off the back. #######.