I somehow doubt I will "cause" the gun to become unreliable.
What he's saying is that it's more likely that the shooter will, due to grip issues or other problems caused by the extreme cold, be the cause of malfunctions than it is that the cold will affect the gun itself.
I can tell you from experience that a Glock without any lubricant at all will not function properly. The slide cam/connector interface will tie up the gun if it is not lubricated. In addition, wear will become an issue without proper lubrication.