I dunno, we really need to see the bottom of the keycap first, to even begin deciding if it's fake or not.
I would say we should presume it to be real, until proven otherwise.
Here is what give me pause though, about it's authenticity: the red color is un-Clack-like due to the bluishness of the red, the convex curvature of the top of the cap is un-Clack-like, and the fact that it is bi-color and not tri-color, is un-Clack-like. However, I am not willing to rule out that it is just a very unusual Clack. I would like to see the bottom.
On the other hand, if it's a fake, it's a very good fake.