I hadn’t seen that - thumb through the trigger guard?
Imagine— horrible as it is— shooting yourself in the mouth with a handgun.
The gun-reversed-in-hand, thumb-on-the-trigger method would “work” “best”.
I wouldn’t get to worked up about about the thumb in the trigger guard. If you are shooting yourself in the mouth, it would be easier to use your thumb than your index finger. It doesn’t mean anything on way or the other.
“I hadnt seen that - thumb through the trigger guard?”
Actually, that makes sense. If he was to point the gun into his mouth, the thumb would be the most convenient means by which to pull the trigger.