Unless the light fixture didn’t simply “happen” to fall.
Use your imagination. 
Hey, she was just networking.
That’s the “law” part but it doesn’t mean it’s not a poor way of handling things. Why should it be no-fault? Why should it apply to off hours even if on a work trip?
I think you are saying the employer can sue the third party, right? That doesn’t help much if he isn’t at fault.