Apparently those charts are from Nvidia themselves, and there is no background information on the tests other than "1920x1080".
I would be suspicious of those results. The games included are skewed toward Nvidia cards, they could have downplayed the AMD cards strengths in Anti-Aliasing and superior memory bus, and its great overclock ability as well.
Also given that the GTX660 is going to be ~$250, while the 7850 is $200. I would expect better performance.
If you follow the links posted in the above you get to the original article.http://videocardz.com/34829/geforce-gtx-650-and-gtx-660-performance-charts