Yeah, that was my bad. The source I looked at (https://franklehman.com/starwars/) didn’t say it was “made as a theme for Finn,” it said it “has the makings of a theme for Finn” and I must have remembered it incorrectly.
It’s probably a case similar to the prospective First Order theme, a discarded leitmotif idea used once or twice in the films as a remnant.