Pretty weak SCG, pretty weak. You talk about the rifle, but fail to mention the more active object, the bullet. A 7.62 FMJ is very different than a 7.62 EHP, one will penetrate with little to no expansion causing very little hydrostatic shock and a smaller wound channel, an FMJ round at max velocity that close could very well have passed through the head fairly cleanly and sometimes without a blood plume. A 7.62 EHP is a very different creature and is designed to cause maximum trauma via massive hydrostatic shock and an equally massive wound channel, an EHP would have done what you are talking about, an FMJ not so much, the video really wasn't long enough to let us see if there was any blood pooling from the head wound, which could be very easily concealed by his body from the angle we are looking at.
I'm not an expert on ballistics, nor do I know the full extensiveness of each variation of a round but from the videos I've seen of a 7.62x39 round being fired, it just decimates concrete into nothing but rubble.