It basically is Supersampling AA. It renders the image at a higher resolution than what is being displayed, then shrinks the image down to the displayed resolution. The result is a sharper image (usually better than MSAA), but takes a lot of extra horsepower to achieve. SSAA gives great results but is the most system taxing form of AA there is.
But no, you were not gaming at UHD resolution. 1080p = 2 million pixels, so 200% would be 4 million pixels (not sure of the actual resolution but is a little more than 2560x1440 which has 3.7 million pixels); where UHD (3840×2160) has more than 8 million pixels. So you would need to be gaming at 1080p with 400% scaling to be rendering at UHD.
amtek
Maybe..
Playing at 100% scaling @1680x1050 doesn't look all that impressive to me, it feels lacking like its not really 1680x1050, too many jagged lines even with 4xAA. But once It's scaled up to 115 or 120% it looks like the game should at that resolution, nice and crisp with no jagged lines.
100% scaling means that it is just running at the current resolution you have it set as, which means that you kind of have the option disabled (100% of 1680x1050 is still 1680x1050). That means you won't see any benefits from the scaling option since you are keeping it at the same resolution. You need to set it above 100% to see any benefit.