The most important significance to the model names given to automobiles is that they are a marketing strategy to increase sales and name recognition. "Mustang" is a well-known model of muscle car, and is associated with 70s-80s American individualism and rebellion. The word comes from the Mustang Horse, which is a classic wild horse associated with freedom and strength; the name was probably selected by Ford because it tested better than other names. Similar powerful-sounding words are selected (Challanger, Firebird) to evoke desire in customers; the more macho or appealing the name, the more likely a purchase and the more likely that the name would spread among potential customers.
The Chevrolet Camaro was actually a direct competitor to the Mustang; its name is a deliberately made-up word that:
...suggests the comradeship of good friends as a personal car should be to its owner...
(Pete Estes, Chevrolet GM, 1966, Wikipedia)
In this case, the word is coined to create a unique brand, one that is intended to compete with other established car lines.
The Toyota Camry is actually the Anglicization of a Japanese word, "kanmuri,' which means "crown," and it was a company policy to name their primary car lines after words meaning "crown," such as the Corolla.
Essentially, car names are picked by focus group, by tradition, or by deliberate design. The main goal is to create a brand that can be instantly recognized, repeated, and desired by customers.