The karate teacher doesn't just block. If you see the clip carefully, you can see that the teacher is rotating his forearm and hit the attacker's forearm slightly at the impact timing. It's not only parrying but also blocking. Then the attacker feel very acute pain. The more powerful attack, the more pain.
Maybe 30secs. is too short... but 1min is enough to catch this idea once you see it. 30 secs. is just for 'Catching' the idea. Of course, you have to spend some time to apply it in real situation. The karate teacher is applying the idea in karate block. In aikido, this kind of technique can be applied to irimi and even in tenkan. But, I bet many teachers will never like it.
ps. I learned it from Rupert many years ago(1999 or 2000??). he he.