I'd say that's pretty much bang on. Here's what the game looks like it you select a resolution with a 4:3 aspect ratio.
That's set to 800x600 and the bars don't quite extend to the left side of the viewport by a couple of pixles and you can still see the gameworld behind is rendered. I'm guessing that all 16:9 aspect ratio resolutions are zoomed in slightly to hide the bars. Could be the setting a 1920x1080 resolution is either rendering higher than that or set to that res then zooming in and compressing the image. Either way you probally won't be getting a 1:1 image at anything other than 4:3.