Well, I don't think it's the case of them not understanding how light works. Just a design trait of all the illustrations that take place in cybespace is that the objects in them should look like they're made up of light (as opposed to something physically tangible). Despite that, sometimes you want dark looking things as well, just for aesthetic purposes. And sometimes it just so happens that something ends up being 'black' and 'composed of light' at the same time. (In this case it ended up as 'black but with some menacing glowy bits'.