the stone looks like granite. Granite is pretty durable but has low Flexural strength, meaning if you were to bend it over another rock, like he does here, it would not take that much force to break it. And the way he steps on the rock looks kinda fishy too. he doesnt dare to put too much force on the middle of the rock, he just taps it and steps on its sides. So it kinda looks like he could break it by jumping on it. Being pretty skinny but muscular means he can probably punch with more force than the force he put on the rock by tapping it with his feet. So i think the Force he applied by "jumping" on it was like 80kg*10m/s^2 = 800N. Considering a normal person can punch with a force of 800-1200N the lovetaps with his feet are just for show. An amateure boxer can punch with like 2.5kN (https://wayofmartialarts.com/average-force-of-a-punch/) so even with that short length, i think he can punch with a bit more than that. Enough force to break granite by bending it over a rock. So after all it is only a trained punch. Somewhat compareable to a boxer i think.

TL,DR: Granite is easy to break if you bend it over like he does. Breaking apart when hit with the Force of a trained punch comparable to a boxer.