Weapons safety Rules in combat

TL;DR: Pretty sure I already know the answer to this, but I got into a dumb Facebook argument and it’s got me second-guessing. Am I correct that the 4 weapon safety rules are still in effect on combat deployments?

Context: I commented on a pic of a Marine holding an M9 — dude had it at a super casual high ready with his finger fully on the trigger. I said something about the bad trigger discipline, nothing crazy.

Guy replies saying I wouldn’t understand because I’m a “boot,” and that during his 13 years of airborne infantry, his whole platoon rolled around with fingers on the trigger while out on patrol during deployments. Said the rules basically go out the window in combat.

I’ve done 6 years in the infantry, "deployed" to Korea but no combat. In my experience, the rules were always the same: finger off the trigger until you’re ready to fire. Blank fire, live fire, urban, whatever, that was drilled in constantly.

So now I’m wondering, for anyone who’s actually been on a combat deployment, is there any truth to what he’s saying? Or is this just another one of those Facebook warriors making stuff up?