My first thought was herbicide overspray... it really does look like that. Arborvitae are sensitive to a lot of chemicals. Hell, my dog is hell bent on trying to kill the lower half of every one that he sees. Amazing how fast dog pee will do that to one. Also, I can see the cleaning agent ending up along the edge of the driveway in concentration, and the roots on that side. Might have poisoned them systemically. I had a neighbor who used gasoline and a power washer to clean motor oil stains off his driveway (which didn't really work) and he ended up doing almost that same thing to some junipers in the process.
Does the homeowner have a very tall dog? Like, 9 feet tall?