The basis for this argument is that human happiness does not come about solely because of money. GDP only measures the market value of all final goods and services that are created in a given country in a year. It does not measure any of the things other than money that contribute to our happiness.
For example, it does not measure how long we work to make our money. Let us imagine that America has a higher GDP per capita than France does but that French people work fewer hours per week and have more vacation time. Which group of people is happier? The Americans may be happier because they have more money, but it is also true that the French may be happier for having more free time that they can spend relaxing with their families. Things like vacation and leisure time are things that add to our happiness and are not captured by measures of GDP.