It makes sense that the pain was subdued due to the release of adrenaline, but at the same time he should be staggering around or showing some degree of pain, right? I mean he expressed his pain quite well when Sangwoo was having his way with him ╥﹏╥
I think we can just call it a convenient plot hole and overlook it ╮( ̄▽ ̄)╭
In the picture where he is running away from Sangwoo because he doesn't want to go out, the korean words there say "limp" (I don't know korean but I read another translation on instagram). So Bum legs are better now but still not completely. Plus the adrenaline definitely helped him not feeling the pain.
So I don't think the author made any mistake
Okay everything else aside, isn't Bum's legs supposed to be broken? How is he able to climb the stairs and stomp around then ( ̄∇ ̄")