That nickel boron coating should be unable to rust, and the Tenifer treated steel underneath should be really damned resistant. Given those two factors, it seems more likely that something else has gotten onto, or into, the finish on that pistol, and has rusted. Some kind of contaminant got in there during finishing. No doubt they'll refinish without argument.
Under the sword lifted high, there is Hell, making you tremble. But go ahead, and there is the land of Bliss. ~ Miyamoto Musashi