I can stealth kill anyone ?

[MojoBreaker]

when i started game, there was option to go to basics tutorial with T-Bug,
one of the tutorial said that you can't always stealth kill, (snap neck) like that heavy armored trooper from ARASAKA,

But ingame i can stealth kill all minions i come across including those heavy armored arasaka troopers

Is this bug or i am missing something, i am playing on Hard difficulty.

 

[Hexipoo]

A lot of things you can do that you shouldn't. Like forcing open doors without gorilla arms for example.