The spin on that shot was due to his contact point being closer to his body than he'd usually like. Also his bodily momentum towards the middle of the court. It shows how adaptable Novak is on his backhand. His adaptability and ability to middle the ball given different feeds are some of the signs of his awesome backhand. Not so much the side spin as it is more circumstantial and doesn't happen that much. Not like Nadal's forehand side spin for instance.
That's the perfect answer for this question.
I'd add - Djokovic's game has this little advantage of him being able to play better the shots when out of position, as he has an extraordinary body flexibility.
For example half the defensive BH slices Federer plays when attacked, Djokovic can bend and twist his body in a way that allows him to actually play a half offensive shot instead. I have actually never seen this in any other player, perhaps Monfils has the body predisposition to play such shots, but he hasn't perfected these as much as Nole.
The Serbian is way more comfortable playing balls on the stretch, rather inside the body.