Backstory (which is perfectly summed up by the comments to the video): BTS was supposed to perform at the end of the show but RM was injured, so their stage was cancelled without notifying BTS (Psy performed instead). So basically they invited BTS and did not let them have a single performance. Army went nuts, so they let BTS to perform off air. Lights out, confetti all over the stage after other singers were done with their performances. BTS was obviously being treated like shit, but they performed this stage just for the Army then (as you see they were in their casual clothes). Apparently RM broke his leg and was in the hospital, so the backing vocals and fans covered for him (with initial guidance from Hoseok). In case you were searching for the video too. The way they wrecked the confetti-filled stage!! They still be doing it!!