According to Neatorama, this is the context:
The Kentucky All State Choir performs at the Kentucky Music Educators Association conference in Louisville every year, and hundreds of the best high school singers from across the state stay in the same hotel. Last year they were at the Hyatt, which has an 18-story atrium. It is a tradition during the conference that at 11PM (curfew time), everyone comes out of their rooms to sing "The Star Spangled Banner." The performance was captured in its entirety on video. This tradition has been going on for at least twenty years, maybe longer.The 2014 conference just ended.