I lived in North Dakota for several years, and I know all about frozen locks, etc. I quickly learned that to use only synthetics, dry lubes, or no lubrication at all if you wanted it to move at -40F. If you used nonsynthetic oils, you had to heat it to keep it moving. We had propane heaters on our diesel engines and electric heaters on the gasoline engines. Gas engines didn't need heaters if they had synthetic oils.
I don't know or don't remember why the locksmith said that, but I took it to heart and never used graphite again. I never liked the stuff.