Since the streak appeared to be maybe 12-18" long, shutter speed was considerably less. Halving the shutter speed to 1/4000 would essentially make the streak 8 inches long at that particular bullet speed. I would venture to say that he was shooting in the 1/2000 to 1/2500 second range on such a nice sunny day, with the aperture at f/8 - kind of a middle-of-the-road aperture setting. ISO probably around 400 to allow for faster shutter speeds.
If you can get the original image file, the camera settings will be included in the EXIF information.
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The post this goes back to references a NY Times photographer stating that 1/8000th of a second was the shutter speed. If true, something besides the bullet, like misted ear matter or shock wave vapor, following the bullet’s path, have to be assumed to explain the length of the streak (too long for that shutter speed if it’s just the bullet). No idea if someone misstated the shutter speed.
https://freerepublic.com/focus/chat/4251335/posts?page=1504#1504