In a discussion the other day with some gamers about my setting, I mentioned the races of my campaign. Rather than describe them in detail, I handwaved them to "human, Neanderthal, tiefling, fire genasi, shifter and shadar-kai." Granted, this isn't exactly true. While the hamazin are definately conceptually the same as tieflings, and the jann are conceptually the same as fire genasi, etc., the shadar-kai is just based on shallow and coincidental resemblances. A more direct inspiration, conceptually, for them is the witches of Dathomir, from Star Wars. And frankly, Nightcrawler (from the X-men) is as important an influence on the hamazin and their look and character as D&D tieflings anyway.
But it brings to mind the notion that there really aren't that many truly innovative and new ideas under the sun, and that execution is really more important than innovation, I think. If you can present something in a way that makes it feel fresh and interesting, it doesn't matter that the idea is very similar to another one somewhere else out there.
It also brings to mind the notion of the "Hollywood pitch" and how great an idea it is. While describing something new, it's often very useful to boil it down to something else that it's similar to and use that to describe it. So, for example, while Eberron is certainly much more than this, it's helpful to describe it as "D&D meets Indiana Jones and The Maltese Falcon."
In other words, rather than making a point of highlighting how my Cannibal Isle inhabitants are different from shadar-kai--and they are, certainly, and have a completely different concept behind their initial genesis--it's often better to focus on the fact that, "hey, they really aren't all that different when it comes down to it." When I say that my hamazin are "tieflings that are like Nightcrawler meets Darth Maul", hey, that's a handy shorthand and someone can immediately identify with and run with.
You can focus on the differences later, when you're ready to dive into the details. First of all, though, a nice, easy to grasp capsule review--often in the form of a "Hollywood pitch" goes a long way towards describing how your setting, game, or any given element of it is supposed to be viewed, without boring any potential audience with long-winded details that they probably don't care about yet.