When the rockets hit the helicopter Nik lost control. Causing Gaz to lose balance and fall out of the helicopter.

You watched in fear as you remained inside the helicopter. You thought your best friend just died...

When Nik radioed Price saying Gaz died you all suddenly hear on your radios. "I'M NOT DEAD NIK I'M HANGING FROM A BLOODY ROPE!" He yelled as he pulled his pistol out of it's holister to use against the enemies.