Disc brakes ain't that great !

Hmmm. Well after a very in depth study of the photograph, I am failing to see what the problem is. As I understand it, you need a brake disc, a caliper, and a set of 2 brake pads. Correct me if I'm wrong, but all seems to present and correct??
It's like a peanut butter sandwich. 2 slices of bread, and a layer of peanut butter. Does the order of the ingredients matter?
 
Could have been done on purpose ?
Instructor: "Remember, we DON'T use the rear brake. Repeat after me . . ."

Paul,
Whatever "instructor" said that is leading riders astray . . .
Shame, shame,shame!