It's not weird if a big guy falls after being hit with a gun butt in his head just because the guy who hit him is light.
It's by no means impossible in reality for someone waaaaaaaay smaller and less strong or powerful to bring down a much larger/heavier/stronger person. I've seen it and i can i can do it. I train in aikido, combat judo and Brazilian jujitsu. when i went to Malaysia in 2006 to train with my Masters Master, he was 83, just under 5ft tall, and nearly blind. I watched him demonstrate a technique which he had developed himself where he (i swear this is no exaggeration) threw around a Japanese man who was attending the class and he was nearly 7ft tall and well over 100kg just by holding his index and middle finger. He did it by forcing the man off balance through his stance and footwork, not fighting the mans resistance but using it against the man, and the pressure points in the mans fingers, wrist, and arm. its ALLL about technique... If you have the training.
No offense, but that sounds like a whole lot of [censored] inspired by Kung Fu Panda

But hey, maybe it's true. I'm not the one to say.