My Lab Joe was 7 when I got Gus, and he was over 100 pounds and Gus was a whopping 14, and after the first five days of Joe growling, glaring, and generally tormenting Gus, he "cracked", and Gus was jumping on him, growling and it was clear, just like in this video, Joe and Gus were having a great time, even though it sounded terrible. They played very roughly for the next four years. Gus was 75 pounds then, Joe was pretty feeble at that point, but he still enjoyed their wrestling.
The ears are a very good give away that the shepherd in the video isn't scared or upset in the slightest.