I agree with
@channington, I think the author's throwing us a red herring and there will be no immediate fight. He's right, Yeonwoo hasn't done anything wrong yet, there's no reason for Taehoon and he start a street fight. Besides, there's the NewTube part - they're not streaming. My guess is that the fight is further down the road, after Hobin finds whatever skeleton Yeonwoo has in the closet. It might have something to do with the fact that Taehoon seems to know Yeonwoo. Probably they were both MMA pros, but never fought each other? (Since Yeonwoo doesn't seem to know Taehoon from before.)
Anyway, Yeonwoo is probably evil because he's working with Seonghoon. And the fact that his father keeps track of his every move also seems suspicious. My guess is that Hobin will be the one to connect all the dots based on info from Taehoon.
@robbi_usammah I don't know whether the bad blood also exists in real life, but interestingly, the wiki on Kyokushin Karate says it was founded by a Korean who emigrated and became naturalised as Japanese. So maybe there's some nationalistic rivalry involved? Or maybe the martial arts are just naturally matched, if Kyokushin is specialised in withstanding attacks and taekwondo, on maximising damage. That would make them natural enemies.