I'm not so sure they were. Even if so, that supposes indigenous people are a singularly unified group.

According to sagas written in the 13th/14th century, a ship was blown off course in about 985, discovering new land but not investigating it. Around 1000, Leif Eriksson sailed west to explore those lands; he named them Helluland, Markland, and Vinland (the islands and coastal bands of North America, likely Baffin's, Labrador, and Nova Scotia/New Brunswick). A few years later, his brother, Thorvald Eiriksson, went back. This is when first contact occured, with the Norsemen finding a drying structure while exploring. The next day they came across nine people sleeping under overturned canoes, so they killed them. Soon after they were attacked by what they called skraelings or something like "wretched shrieking people" in Norse. Thorvald would die there and the third brother, Thorstein would launch a failed expedition to retrieve his body. Thorstein later died of illness and his wife married Thorfinn Karlsefni who then took his family and attempted to settle in Vinland They had somewhat good relations despite the initial troubles and it is likely they were dealing with a different tribe than Thorvald had. They encountered one another in odd ways, the natives waving sticks and the Norse raising a white shield. It was an attempt to communicate and trade soon followed. What happened next is, according to some, a different tribe finding/learning of the Norse settlement and attacking, causing Thorfinn to return to Iceland and abandon the settlement. All we know comes from the sagas, so it is unclear exactly who attacked or why.

This same saga plays throughout the New World. When Cortez arrived in South America, he was greeted. Then he allied with some tribes to annihilate others and did what he wanted. Juan Ponce de Leon, who had sailed with Columbus on the second new world voyage, did the same in the Caribbean and Florida. The English saw the same in Virginia, when Wanchese and Manteo helped the original (temporary) and second (failed) colonies at Roanoke and returned to England to bridge the language (and culture) gap. It was later in a raid Manteo's mother would be killed by Anglo settlers. Likewise in Jamestown and John Smith. Likewise for the starving, dying Pilgrams at Plymouth when Samoset walked into the settlement, said welcome, and asked for a beer. Less than six months later, the treaty he brokered with Massasoit and Tusquantum in March of 1621 would lead to what we call Thanksgiving. This is despite Tisquantum himself being enslaved by a captain left after the exploration of John Smith to further native-anglo relations. Instead, he enslaved many Wampanoag and Nassuet people, took them to Spain, and sold them. (I'll also add Tisquantum later died from "Indian Fever" or European disease)

There is a very long history of peaceful first contacts. It is typically after the Europeans initiated violence that relations deteriorated. Amd this says nothing of the disease we brought, killing as many as 90% of North American Natives. That alone undoubtedly made some tribes weary as they saw trade bring death.

To your question, though: the source is a verbal saga recorded 200-300 years after the fact. Even so, it details a violent first encounter with a peaceful, and sleeping, group of natives.

The Sagas of Erik the Red and of The Greenlanders are the source works.

See In Search of First Contact: The Vikings of Vinland, the Peoples of the Dawnland, and the Anglo-American Anxiety of Discovery by Annette Kolodny for more in depth study of the native encounters with Vikings and Europeans.

E: typo