Do you even know what this article is about? It's about a device that has an array of microphones and a downward-facing wideangle lens. You look at a screen with the view from the camera, click somewhere, and the device automatically singles out that small area to pick up sound from. It's automatic. Not done in post-production. Automatic.
To "improve" it in post-production in the way Man Eating Duck used the word "improve" would be to use the recordings from the microphones to manually single out a particular area. Manually. As in, not automatic. So "Assuming that it's not been 'improved' in any way it's really quite impressive" means "This thing is damn impressive... as long as it actually works the way the video says it works -- automatically (not manually) -- and they didn't do it themselves in post-production."
Clear enough for you?