The problem there is that he didn't focus on the mirror - as shown by the fact that the edge of the mirror is OOF. This is where we get into the physics of light, and the way things work isn't obvious at first.Your week one confuses me!
As I understand DOF, you focus on one point in the frame that is a distance from the lens and (subject to lens and F# etc) things in the foreground and background are OOF. So, if you focused on the mirror and the image it produced, why is the mirror image of the candle OOF?
Dispite this, I think the shot works and it's a great take on the week 1 theme.