That's not what it is. It's obvious if you follow these guys that they are Apple fans who wanted to customize their OS, couldn't, so created their own. They used OSX as a starting point, that's for sure, but that was years ago, now it's going in its own direction. I personally wouldn't use Elementary because it's overly opinionated for my taste, but I recognize their hard work and originality, they are not ripping anything off and haven't for a long time.