I think hitting a car is bad, but how else does the other person back out of their driveway? Maybe it would help if you just think of each car pulling forward and hit, whose fault would it be then? Who has a right of way, whoever is in the street first? No, stop signs in a driveway.
There is no such law, as you may need to cross the yellow to end up facing your proper direction of travel after you leave your drive.
So you were both backing? In short, if that is the case, it's should be determined you were both at fault as the reversing driver most always has the greatest duty to yield. The big question is how much negligence they place on each party (50/50, 70/30, etc.) Honestly it can be fairly arbitrary.
In addition to who crossed the yellow, the adjuster should also note where the damage occurred (i.e. who hit who). Even if the driver that backed across the yellow had damage on their passenger door and fender, and the other driver had damage on their rear bumper and deck lid (as pictured), I would place the majority of negligence on the party with the rear (not side) damage. Sorry bud.
Actually, the instruction (which appears to be from the driver's license book) does look to be relevant. It says to back into the lane closest to you for the direction you'll be going. The picture shows what appears to be a four-lane road. The silver car backed through the closest lane and into the further lane.
Whether the DL manual constitutes binding authority is another matter, but at the least, I'd think it persuasive in assigning relative fault.