As I see it, "arming the ball" means to generate most, if not all, of the racket speed/power, using (only) the shoulder/arm. This is not what Novak is doing. He is using a full kinetic chain. It start with his lower body and transfers to the hips, then torso followed by shoulder and arm.
Notice that, as his racket is dropping (prior to the forward swing), his torso is coiled more than his hips. This means that he has energy stored in his core. The hips uncoil followed by the torso. As the torso catches up and passes the hips, the energy stored in the core is being released/transferred. At the start of of his forward swing, the racket head lags -- the arm/racket is being dragged by the uncoiling torso. There is tension/energy stored in the (right) pectoral muscle. As the forward swing progresses, the stretch in the pectoral muscle is released and the energy is released/transferred to the shoulder/arm. As this transfer happens, the arm starts to move faster than the uncoiling torso.
The kinetic chain for this FH is actually a bit more complex than I have described here -- I have just highlighted some of the links and transfers of the chain (of events).
Every tool is a weapon -- if you hold it right. (~Ani DiFranco)