Who said he didn't? The rpg-7 isn't known as the most accurate weapon.

That was what I was thinkinghit the tail rotor. Sort of like 'Black Hawk Down'.

It could have survived where he hit it. He should have aimed at the tail rotors or main rotors. No matter how tough the bird is, the rotors are the weakest parts.
Oderint Dum Metuant

It's possible that a shaped charge like an RPG could simply blow out the other side with minimal damage to the helicopter itself, but I'd wager the pilots would be deaf, at the least.
I can't speak for Russian-made equipment, but having been both a US Air Force Weapons Systems Officer and a US Army Armor officer, I can say that both USAF flight helmets and US Army tank crew helmets have very tight-fitting padded radio/intercom earphones. These are well sufficient for protecting the wearer's hearing from jet engine noise and the blast of a tank main gun, the latter of which is much louder than a grenade detonation.

It's possible that a shaped charge like an RPG could simply blow out the other side with minimal damage to the helicopter itself, but I'd wager the pilots would be deaf, at the least.