It's totally not clear to me why finding that the amendment was motivated by bigotry would invalidate it. I assume it has something to do with the distinction between an "amendment" and a "revision"? (The former can be passed by ballot initiative in California and the latter can't.) But I don't see why the motivation, rather than the content, of a proposal can make the difference between whether it's an amendment or a revision; and the article doesn't really explain why the judge thinks it should matter.