California has high life expectancy and above average educational attainment, so the issue might be income inequality. The gap between average earnings and median wage is bigger than any state except New York.
The time is low to match with the other US state quizzes. I do agree it is low however (especially for a non-American, I wish I could modify the time a little depending on which country you took this from haha).
The methodology is not a problem, the qualities measured by the HDI (such as per capita income, health or average education) are measurements you can measure tangibly. However, using the HDI as a basis for quality of life is still flawed. The inequality-adjusted HDI attempts to remedy this by looking at the average person, rather than an aggregate sum of a society, and this index is quite punishing towards the US as a whole for its inequality (at least compared to other developed countries).