There are 3 braces that are the same, only one differs. Maybe he didn‘t catch that. You are not missing anything, the rail is on the back and there is no way to make it magically disappear. 
I used to have 750x550mm, but that was a bit too much, there was chatter in the middle of the workspace. I know reduced it to 400x400 workspace, but it‘s only a plotter now.
You can find more information here: MPCNC Primo Schneewittchen Reanimated - Oldenburg, Germany, there‘s everything to know.