Correct. Variation is natural. Compasses vary depending upon where one is. Deviation is caused by electro-magnetic fields, magnetic materials, iron pots and pans, engine blocks, Steel hulls, etc.
Nature varies, man deviates. It's also why the magnetic compass is used in dead reckoning. Sooner or later every sailor who depends upon it will be dead; hopefully from natural and not deviant causes.
Doubtless your previous correspondent was navigating by solar fixes, or perhaps using a Bumstead Solar Compass.
Wrong again, I'm afraid. My pevious navigating was through the use of cellestial, DR, INS, Doppler/Airmass, Pressure lines of position, Consolan, Omega, drift meter, and various other methods. I was a P-3 Patrol Plane Mission Commander and PQS instructor navigator in the US Navy, which, you'll have to admit, has a fair amount of practical navigation under its belt.
BTW, DR comes from deduced, not "dead."