PixelBasher doesn't do any automatic shading. What you see in the video's posted on social media: It's more like overlaying gradients or textures and then limiting the number of displayed colors. PixelBasher does ship with a few fancy dither patterns to simulate rust, dirt, etc.
In the end it's only one of the tricks that PixelBasher has. If you want to test if this method could work for you, I think you could also manually try to do something like that in another application.