Getting back to the original question of who is at fault, if the guy backed into a stationary object, it's his fault. Around here, you're not supposed to back up unless you can do it in safety, which, obviously, he couldn't have done.
2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg
And remember folks, Only You Can Prevent Hilliary.