You weren't driving on the 580 by chance, were you?
My friend was driving on the 580 on his way to brentwood and somebody threw a 8 pound spool of wire from a construction site off an overpass, and it went through his windshield and broke his arm. When he got to the hospital, there was also another person that was there and was shaken up from the same thing. A few days later somebody did the same thing to an ambulance.
Be glad that's the only damage. My friend had to get a stainless steel plate screwed to his arm.