That gun has wartime German wooden grips and a Waffenamt stamp. The Germans were not bothering with nickel finish. OTOH, these guns were very cheap in the 1950's and 60's, nickel and chrome plating was more cheaply available than now, and many people thought it was an improvement compared to the drab or worn original finish. Anything can happen, but having that turn out to be factory nickel would be like winning the lottery.
From what I recall, FN 1910's (the same gun with a shorter grip and barrel) were offered with a factory nickel finish. The factory always left the trigger and safety catch blue (or black, IIRC). Pre-WWII FN 1922's were generally military or police guns, so offhand I don't know if the factory offered them in nickel.
BTW, FN made motorcycles back then. The nickel plating was done by the motorcycle works on an "if and when" basis, so pre-war nickel plated FN pistols are scarce.
All this is per my recollection of the books about FN pistols by Anthony Vanderlinden.