That's what they speak there. Just about everywhere else in Latin America speaks Spanish, but they speak Portuguese in Brazil. It has to do with a Papal decree back in the 1500's that divided up South America between Spain and Portugal, who were fighting over colonization rights.
I thought it had something to do with Spain getting everything west of a certain longitude and Portugal everything to the east, which is why the Spanish colonized Africa and spain the Western hemisphere; but they didn't figure that there was any land that straddled that line (i.e. Brazil)