Side/window Air Bag problems of the 2000 BMW 740

While driving on the highway, a car in the other lane hit a piece of firewood and knocked it under our car. This caused (for some reason) the passenger side airbag on the door (the side airbag) to deploy. When it deployed, it tore loose a strip of decorative metal on the interior. The strip was about 2-3 feet long and had between 3 and 5 1" bolts protruding from it. The metal strip hit the passenger on the arm and caused an abrasion. We were greatly concerned about this for two reasons: (1) why did that particular bag deploy when there was only damage underneath the car and (2) the metal strip that ripped off could have hit someone in the eye or in another place that would cause a serious injury. Even as it was, the passenger's arm was totally bruised from wrist to shoulder. This information was provided to the dealer and the BMW complaint department, who told us we would hear from them within 3 days. This was 4 weeks ago, so we obviously are not going to hear from them now.