Not necessarily true. Show me video of this incident.
For the dog to “pin” he student, the dog was either on its hindquarters with its front legs on the student, or the student was on the ground, with the dog’s forelegs (or all four legs) upon the student, preventing movement.
A direct shot from either position would leave the student in the direct line of fire.
I personally suspect that the commenter is unaware of the difference between “pinning” something and “cornering” something. But since the commenter used the word “pinned”, it must be assumed that is what the dog was doing.