No, they are in fact not related to normal pigs, even though their name suggests so.

Here's an excerpt from Wikipedia, which explains it more thoroughly;

"Despite their common name, these animals are not in the pig family Suidae, nor do they come from Guinea in Africa; they originated in the Andes of South America and studies based on biochemistry and hybridization suggest they are domestic, not wild, descendants of a closely related species of cavy such as C. tschudii."

Their wild ancestors are unknown.

So a more suitable name would be Andes Cavy. ;-)

Yes, or something like that. :)