I'm surprised he didn't even try teaching the clinch, TKD has excellent kicks but its relatively weak close-quarters combat, so clinching knees, elbows would be pretty good as a counterattack
If I know this manhwa (and I do), we'll get in the next one a flashback to Chickenhead's video explaining how him getting punched in the nose was all part of the plan.
I think taekwondo guy's reason why he quit is because of his love for taekwondo's kicks. He was nicknamed standing striker, probably because he punched more often than he kicked. This could also explain why he was so miffed when taekwondo was belittled, he probably loved it too much to keep on winning UFC?