Why is a guinea-pig called a guinea-pig when it comes from South America not Guyana or Guinea?

They may be called guinea pigs because they weighed a guinea or because they were sold for one guinea. People may have also thought that they came from Guyana or Guinea. Another reason is that the first person to own or sell or discover them might have been named Guinea.
well back in south america, when guinea pigs were a delicacy, the south american's money was called the guinea. so when they sold guinea pigs to each other, the guinea pig was sold for a guinea. the 2nd half of their name is because of their piggish manner. Lauryn24-I think they are called the guinea pigs because it makes somewhat similar sounds like that of a pig and is also almost built like a pig, a large head, a stout neck, a smaller body in relation to its head and neck and a tail of very little consequence. So it got is name from a skinny pig to a guinea pig.
The etymology of guinea pig is unknown and confusing.

Despite its name, guinea pigs are not from Guinea nor are in the pig family. They are native to the Andes Mountains in South America. They are believed to have been called pigs because their structure is similar to that of a pig's body. The guinea part of the name is even more confusing. There are three theories: one is that the guinea pigs were brought across the Atlantic Ocean to the island of Guinea then to Europe, another is that guinea was used because it is a word in the English language that means "far away land", and a third is that it was a variation of the word "Guiana", a region in South America (composed of Dutch Guiana [now Suriname], British Guiana [now Guyana], and French Guiana [still present]).
Some people say that guinea pigs got the "guinea" part of their name because when sailors brought them from South America they sold them to people for a guinea as pets. A guinea is like a foreign dollar. They got the "pig" part of their name because the squeaking noise they make reminded them of baby piglets.

How the animals came to be thought of as "pigs" is not clear. They are built somewhat like pigs with large heads relative to their bodies, stout necks, and rounded rumps with no tail of any consequence; some of the sounds they emit are very similar to those made by pigs, and they also spend a large amount of time eating.
The guinea in guinea pig comes from the fact that guinea pigs were brought to Europe through New guinea , though in fact they originally came from present day Ecuador and Peru.