No, this is Klein's dream. He's "asleep" while contesting the former Lord of The Mysteries for control and the dream is just like a projection of his inner thoughts. Because it's his dream, the people are all people he's met before during his time as Klein but is in the world of Zhou Mingrui since that's who he really is. I'm assuming the people are the sequel's protagonists here to "awaken" Klein from his dream.