What a pretty cat!
I have seen articles on winged cats, and nobody seems to know exactly what causes it. Wikipedia has a good entry about them. They have been reported for many years all over the world.
The article appears to be removed now, but I have read about cats around the world that have supposedly been born with fur-covered wing-like appendages. I don't think they are considered "real" wings per se--they just resemble them. They may be just a genetic freak of nature, IMHO. (Or the pics I've seen have been faked?)