How do cold air masses reach South America?
The Pacific coast of South America is affected by the Humboldt Current, a wind-driven "upwelling" system running counterclockwise that is cold and windy but nutrient rich..

The "six o'clock" position indeed touches Antarctica, and then the right edge of the "clock" reaches Chile, Peru, Ecuador, and Colombia, as far north as the Galapagos Islands near the equator, making those areas cooler than equivalent latitudes on the Atlantic coast.

The reason the currents don't "originate" in the Antarctica is because they are part of a circular system that spans a whole ocean in the southern hemisphere. But they "make stops" there.

The ocean and atmosphere mutually interact to create a "coupled" system that brings about the so-called ENSO El Nino (La Nina) Southern Oscillation, with its characteristic weather changes.