His legs still haven't fully healed. The sfx say "limp" when he was running into the room. Adrenaline rush could have caused him to feel less pain in the moment.
Bum never told Sangwoo his uncle raped him so Sangwoo wouldn't know.
His leg has bandages in 19 and I remember that Sangwoo knows about uncle and about rape
Ah, maybe Koogi forgot to draw them.
I remember Bum telling Sangwoo that he lived with his uncle and nothing else. The only time "Sangwoo" mentioned the rape was in chapter 7. However that was only an illusion in Bum's head.
Bum's legs are hurt in 19 and not in 20 and Bum is not virgin he's uncle raped him and this chapter is no good I didn't like it. I was waiting good shits from season 2 but no #－.－)