That's the source I used. I also checked the primary source cited on Wikipedia to make sure it was correctly cited and confirmed that it was. As you write, the Wikipedia article for Mumbai indicates the lowest temperature ever recorded there was 11.7°C (53.1°F), which is clearly above freezing. Thus, clicking on Mumbai in response to the fourth question will cause you to lose a point while not clicking it will cause you to get a point. I took the quiz and confirmed that this is what happens.