Las Vegas is the home of the NHL's Golden Knights. They have a good team, and they're very popular with the locals. I was there once to support their opponents, and the Knights fans were out in force. (My team lost, but whatever. It was a great game.) When singing the national anthem before the game, they placed a heavy emphasis on the "Gave proof through the KNIGHT!" line of the anthem.... I suspect this group was a bunch of Knights fans, singing the National Anthem outside before a game. This looks like the outdoor area where fans wait to get into the stadium. Listen again. At the end, you can hear a few shouts of, "Go Knights!"