...who also happens to be a Special Forces Soldier...
Hmmm... How long did you talk to him before he volunteered that information?
Shooting at the pelvic girdle is a tool in the arsenal. I'm not aware of any reputable trainer teaching that the pelvic girdle shot should be taken in preference to a COM shot, just that it's an option that one should be aware of.
As pointed out, removing the mobility of an opponent armed with a firearm will not stop him from firing back, but it could be a useful option when engaging a determined attacker with a contact weapon (e.g. knife/club/etc.)