I don't think so. Shooting an animal in the head once you've slaughtered it would be redundant. As Fadi mentioned, I think you're confusing it with stunning the animal prior to slaughtering it.
I'm guessing that old mate is probably speaking from experience, what is your background with respect to the subject matter?
I'll leave the relevant quote here for your perusal.
Knowledge on aus halal came from working with halal meat in Australia and Aqis and the operations in our kill houses/ abattoirs...