Yep, I think you have got it right. It looks like a large amount of structure was deformed or opened up by the pressure wave (the crown skin in other pictures is pressed in between frames), and the impact with the ground has caused it to splay out.
From the account of the B-52 flier here and some other pictures around of SAM damage it does appear that the missile was extraordinarily close when it fused.
The front of the cockpit looks like such a strong structure, too.