Ditto above...some aftermarket or left over wiring from a previous owner's install was the first thing that made me go hmmm. I can't ever recall BMW grounding anything with a screw...plus BMW normally uses a brown wire for ground and it usually runs back to some grounding point (like one of the usual ground connectors or combs).
See #2 & #4 below...these are comb connectors which can usually be shortened to the desired amount of poles...this is what you see multiple ground wires connected to around the vehicle:
{here's another example of how BMW groups a bunch of ground wires to one large connector "comb"}
