Here's why:

* Oceanic Crust: The South American plate also includes a large section of oceanic crust to the west of the continent, making up the eastern portion of the Pacific Ocean. This is evident in the presence of the Peru-Chile Trench, a deep oceanic trench where the Nazca Plate (an oceanic plate) subducts beneath the South American Plate.

* Subduction Zones: The subduction zones along the western edge of the plate are clear indicators of the presence of oceanic crust.

So, while the South American plate is primarily associated with the continent, it also includes a significant portion of oceanic crust.