That was really stupid on so many levels.
The guy wanted to fight the MC. Okay. He proceeded to fight EVERYONE ELSE in Group B with relative ease by just attacking them. He couldn't do that with the MC? Yeah, the MC didn't attack when the guy poured water on him, but the guy could've just been the first attacker. There was literally zero explanation for why he couldn't just attack the MC to start the fight. Maybe he thinks it's boring? Because it's dishonorable? No explanation. Zero.
And then it says that's the martial arts that can kill? A LOT of martial arts can kill. Many of them are designed to kill. It would've been so much better if the guy said something like "that's one of the deadliest forms of martial arts!". Imagine if there were a lion running loose and someone said "A lion? That's the animal that can kill!" That's how stupid that sounded. Yes, it's correct. It still sounded stupid.