That's a very old strategy called jittering (also see stochastic gradient descent.) This is something entirely different. They are not doing regular backpropag

That's a very old strategy called jittering (also see stochastic gradient descent.) This is something entirely different. They are not doing regular backpropagation at all, but somehow using neurons to learn how to backpropagate values. I haven't read the paper yet, just read their slides earlier, so that might not be correct.