The study found that Democratic counties, like Holmes County, Mo., which is on the higher end of the giving spectrum, provide more over all to charitable causes, but through a combination of what the authors call voluntary giving, like charity, and involuntary giving, which the rest of us call taxes.
What this paragraph implies is that Democrats give more (as a whole) through their acceptance to pay higher taxes, which goes to help others. This could mean even more money is distributed to the poor by more people, even those each quantity is lower per person.