The props don't turn that slow, it's just an optical illusion from the camera and the real rpm of the props.
The thing that mystifies me about the parts of that video which show the props going round very slowly is that (a) the blades appear to be in the feathered position, and (b) they are exhibing none of the interlacing effects which one normally gets with fast rotating objects on high scan rate HD video. So I then wondered whether in fact these are slow-motion sections of video; however, given the very high speed of the Bear's engines, it would need to have been slowed down by such an amount as to noticably affect other aspects, such as the speed of the Typhoon's strobes and the pan rate of the camera, both of which appear normal.
Is it out of the question that the Russians did in fact turn off/feather the engines on one side (and then the other) after all; presumably a Bear is perfectly capable of flying on two, albeit on the same side?
I probably need to have my coat ready for a quick exit....