No, that is not true at all. There was a wide variety of nomadic and semi-sedentary indigenous groups in present-day Argentina, Chile and Uruguay (the "Southern Cone"). The arrival of European settlers in the sixteenth and seventeenth centuries displaced many of those groups, while bringing others into complex cultural and economic exchanges with the Spanish settlers. There is a lot written on this, but for general survey you can look at the anthology "The Cambridge History of the Native Peoples of the Americas" (http://www.cambridge.org/us/academic/subjects/history/history-native-american-peoples/cambridge-history-native-peoples-americas-volume-3-part-2)

Hope this helps.