Beats me. Ferrocerium is a "correct" term and at least it is descriptive of the majority of the composition (Cerium, perhaps with some other rare earth metals, hardened with black iron oxide). The other term seems to be in some use also, as you noted. I suspect that the other term is an accidental vulgarization of the original term coined by the inventor. <shrug> Again, I'm only sure that ferrocerium is a correct term, not that the other is "wrong".
Tom