only a few other ways you did it.
1. sound trigger? - probably not
2. really fast reaction time and luck? - possibly
3. using your frames per second in your camera body? unless you had d300s/d700 with grip or D3x/s and still good reaction time and luck might be kinda hard still shooting bullets
reason i said long exposure (3+ seconds stopped down with ND filter) is because of the blur, since i cant se your Exif data to see the exposure (i dont use browser plugins to read that only FLickr if people link it)
even with shutter speeds close to 1/1000 you might still get some blur since bullets and fragments move so quickly.
please share how you did it.