I can't give a definite answer because the definition of happiness varies from person to person. Qin Fang and Si Teng might feel happy living in seclusion in Cangcheng Mountain because they could stay away from the hustle and bustle of the city and enjoy a peaceful life. But if their lifestyle and values are different from those around them, they may feel lonely and dissatisfied. In addition, happiness also depended on whether their personal goals and expectations were met. In the novel, Qin Fang and Si Teng lived in seclusion in Cangcheng Mountain to pursue inner peace and freedom, not to escape the pressure and difficulties of real life. Therefore, whether they are happy or not depends on how they define happiness and whether they achieve their personal goals and expectations.