It is my understanding that this claim about Americans' charitable giving does not disaggregate giving to food banks, Girl Scout cookie drives, political causes, the environment, cultural events, religious institutions, etc. Much of this charitable giving does not feed the hungry or house the homeless.
Plus the fact that there’s bias in the first place - citizens in a country where they know social programs will care for their needy would not need to donate.
Purchasing Girl Scout cookies isn't counted as a charitable donation.