Which taxonomic detail makes the name 'guinea pig' inaccurate regarding the swine family?

Answer

They belong to the order Rodentia, family Caviidae

Guinea pigs belong to the order Rodentia, family Caviidae, meaning they are entirely unrelated to pigs (swine family).

Which taxonomic detail makes the name 'guinea pig' inaccurate regarding the swine family?
animalOriginguinea pigPeruvian