It is a port, but not a direct one. The gameplay and storyline has been altered significantly. It's basically the latest in a long line of FarCry games intended to milk the cash cow as much as possible.
The original FarCry on PC came first, then FarCry: Instincts for the xbox. Then soon after there was a sequel called FarCry: Insticts - Evolution. As if to confuse people even more, they then merged Instincts and Evolution and turned them into a 360 game called FarCry: Instincts - Predator. After that came the Wii version, Farcry: Vengeance, which is absolute sh**e. Now there is Crysis in the works and an expansion pack due for the original FarCry.
I hope that clears up any confusion about the different games and sequels.