I think this is the Wikipedia page you are referencing:

The Fuegians have been thought to be physically, culturally and linguistically distinct from other Native Americans. Some proponents of this theory suggest they may be the descendants of Australian Aborigines who colonized the area prior to the arrival of mongoloid Amerindians. Further credibility is lent to this idea by research suggesting the existence of an ethnically distinct population elsewhere in South America. Both Tehuelches and Selk'nams practiced body painting and rock art similar to that of Australian Aborigines. In contrast to most Amerindian peoples, Fuegians appeared to be taller than most Europeans (this does not include the Yaghans, who were quite short with skinny limbs and fat bodies - a physical adaptation to the cold, or the Kawesqar).

As the article states, the people of Tierra del Fuego look and act very differently despite living close to one another in a small geographic area. Some peoples were very tall and muscular, were land hunters living off guanaco, and preferred to use bolas and later bows to hunt; others were shorter in stature, lived near the coasts, hunted marine wildlife using harpoons, and traveled in canoes. The Wikipedia article quoted above links to this page published by the BBC in 1999, which references several highly controversial theories about the peopling of the Americas as evidence for its Australian origins hypothesis. It mentions the Luzia skeleton and an archaeological site found in Eastern Brazil which seems to have human habitation that radiocarbon dating shows occurred 50,000 years before present (neither of which are accepted by scholars). The article only references Tierra del Fuego by contending that the faces of modern indigenous people in Tierra del Fuego resemble Aborigines. It also proclaims that rock art practiced by Fuegians is similar to rock art practiced in Brazil (no examples, scholars, or references are provided). Then, the article jumps to the conclusion that Fuegians are the only remaining South American descendants of the Australian Aborigines who were once found in Brazil and presumably all over South America.

I tried to find works by scholars who believe in the Australian hypothesis. I only found Portuguese anthropologist Méndez Correa (in the 1920s) and French scholar Paul Rivet (1943) who argue that Aboriginal origins explain the many cultural differences of certain Fuegian groups. Additionally, I tried to find references to Fuegian languages being related to Australian indigenous languages, but all Fuegian languages are related to Chono, Mapudungun, or Kawésqar, with the exception of Yaghan, which is considered an isolated language. I searched through recent books and articles published in the last thirty years on the peopling of Tierra del Fuego, but I could not find a single peer-reviewed work that asserts that the differences between certain Fuegian indigenous groups were the result of contact with or settlement by Australian Aborigines. There simply isn’t archaeological evidence that this is true. One can point to cultural similarities between different hunter-gatherer populations on both sides of the Pacific, but those similarities do not prove Australian origin. Unless hard evidence is found, the similarities are merely coincidental.

According to a study by Carlos Lalueza-Fox, Alejandro Pérez-Pérez, Eva Prats, and Daniel Turbón published in their article “Linajes mitocondriales de los aborígenes de Tierra del Fuego y Patagonia,” despite their physical differences, Fuegian populations have the same class of mitochondrial DNA with all the same markers. So it is clear that regardless of physical differences, genetically they are not significantly different. Despite this evidence, some bloggers like to include sentences on their blogs something to the effect of “some DNA studies show that Fuegian populations have Australian DNA” but they never cite any actual studies. I looked, but I haven’t been able to find any studies from a peer-reviewed source that indicate Fuegian people have significant genetic similarities with Australian Aborigines.

So what then explains all the differences that existed in Tierra del Fuego? According to Ernesto Luis Piana and Luis Abel Orquera in their article “The Southern Top of the World: The First Peopling of Patagonia and Tierra del Fuego and the Cultural Endurance of the Fuegian Sea-Nomads” published in Arctic Anthropology, the significant differences between Fuegian groups makes sense in geographic terms. Tierra del Fuego has two distinct physical environments: The southern and western coasts are steep and mountainous, have many trees, but are not home to many big animals; the northern and eastern parts of Tierra del Fuego has large grassy plateaus filled guanaco herds. People on the coast used the wood to construct canoes to hunt plentiful marine wildlife; whereas, groups to the north and east hunted guanaco on foot, only occasionally using sea resources. Archaeologists can also trace the evolution of Fuegian toolkits and cultural items to earlier Fuegian sites and even earlier migrations from Patagonia.

Anthropologists and archaeologists debate what exactly the differences in lifeways indicate about the process of Fuegian settlement. For example, Carlos Ocampo and Pilar Rivas argue in their article “Poblamiento temprano de los extremos geográficos de los canales patagónicos: Chiloé e Isla Navarino” that Fuegian differences may be the result of different waves of people coming into the area. Piana and Orquera argue that populations of land hunter-gatherers diverged into two distinct populations--one that favored sea resources and one that favored land resources. In either case, there is not evidence that these differences were the results of Aborigines managing to cross the Southern Ocean and landing in South America to create two distinct populations.