it depends on how far out you were (wether or not you had established yourself as reversing or if you speedily reversed), if you had 3/4 of your car out when they hit you, i dont think it would be your fault as you would've established yourself as reversing, and at this stage, it would be reasonably forseeable that you would have right of way and that anyone coming would give you way while reversing.
if you were around 1/3 - 1/2 of the way out when it happened then they might see it as you reversing without looking or paying any attention to your surroundings.