It can be a combination of the two.
Using a relatively small, low power bullet like the 7.62x39 in a standard configuration, the damage you see is almost impossible.
The same round jazzed up though, you MIGHT come close.
A 14mm round on the other hand, in its standard configuation, could in fact do this damage and more very easily. Souped up, you could probably take off the whole head, not just a portion.
The point is, in this case, it is unlikely that the damage was caused by rifle seen in the previous photo.
Not so Al. A high velocity round in the brain will blow the head apart like shown. I've seen it done with an M-16. The human cranium is designed to withstand preassure from outside, not well over 1000 foot-pounds of overpressure shock from the inside that would be imparted by a chicom military round.