While that's a good point, I'd have an easier time believing it if Kain hadn't remained Kain in every subsequent English-language reissue of the game (that I'm aware of, anyway). The odds that he wasn't intended to be named after the Biblical character are so minuscule as to defy comment, especially since the Romanisation of his name is in fact spelled "Cain" in some Japanese materials. It seems more likely that FFVII and FFIV have simply been handled differently when it comes to character name translations.