No, Siam and Vietnam are not the same country. Siam is the former name of Thailand, while Vietnam is a separate country located in Southeast Asia.
Historically, Siam was the name used for Thailand until 1939 when it was officially changed to Thailand. The name Siam is still sometimes used to refer to the country in a historical context.
Vietnam, on the other hand, has always been known as Vietnam. It is located to the east of Thailand and shares borders with China, Laos, and Cambodia. The two countries have distinct cultures, languages, and histories.
In summary, Siam (now Thailand) and Vietnam are two different countries with their own unique identities and histories.