This is a strange and intriguing video. This martial artist uses his own method of conditioning and what I like about it is that he is training strength into his body with the least tension as possible.
I would have to speak to him to find out why he uses the grunting… it may be to manipulate breath in his belly, using Ujjayi breath that I use in my home study course.

Watch him and notice how loose he looks after the moves and how he focuses on 3 dimensional movement.
Try this when your working out next but maybe not the grunting as you might get taken away by the men in white gowns:)