Is that what their insurance/their lawyer/they told you, or what an independent lawyer or expert told you? That doesn't make much sense to me, but many laws do not I guess.
If the guy had kicked up a rock from under his tire, thats a different story. That debris/rock/whatever was already there, he just happened to hit it, and you just happened to be the poor sap behind him. But thats not what happened here.
If I'm driving down the road with propane tanks, one rolls out of the back, hits the ground, and someone hits it and it explodes... is that just a road hazard? I know its an extreme example, but its the same logic. Someone's carelessness caused an object that wasn't there before to be there, and not only be there, but cause damage.
There is a thread here somewhere on the forum where a guy's new truck get peppered with shattered glass on the highway because a glass company didn't secure a large pane of glass to the side of their van properly
StarknightMT windshield, and it fell off in front of him. I believe their insurance took care of his repairs.