"Flush to the wall" says to me that the front surface of the TV lines up with the drywall or whatever the surface finish is. That is, if you're standing off to the side of the TV, when it's packed away in the wall you can't see more than thin lines that outline the face of the TV... or the frame.

So the entire depth of the mount plus TV are positioned such that none of it protrudes out of the wall when it's put away.

I'm pretty interested just to find out how it's done!