Because he either lied or Air Taser's home page lied:
The recommended stun device self-defense technique is fairly simple; drive the device into the upper shoulder, stomach, groin area, or other sort of muscle area such as the neck or kidney, and then pull the trigger.

1) A short burst of 1/4 second duration will startle an attacker, cause minor muscle contractions, and have a repelling effect.

2) A moderate length blast of 1 to 4 seconds can cause an attacker to fall to the ground.

3) A full charge of 5 seconds can immobilize an attacker, causing disorientation and loss of balance. Attacker may fall to the ground, weak or dazed for some minutes afterwards.

http://www.airtaserandstungunstore.com/training.shtml

Rainsong