His depth of field explanation may be valid, or may be a CYA after-the-fact claim, but there again, losing a clear background means some sacrifice was made. It all seems odd, but then I'm not much of a photographer.
Also of note (the video may clarify, but most headlines don't), the streak is not the bullet, it's a condensation trail. The bullet itself would only leave a 4" to 5" streak at that shutter speed, and would probably leave an identifiable but faded image of the bullet itself.
[2700 ft/sec x 12 in/ft x 1/8000 sec = 4.05 in of travel, plus bullet length]
I was surprised at the 24mm focal length. He had to be close or the picture cropped a bunch.