The description of the video claims that "Tribe in Papua New Guinea meets white man for the first time. Filmed in 1976. They have never seen modern civilization, or any modern technology." First of all, it is not from 1976. The date is incorrect on many videos because, most likely, someone misread the following disclaimer, at the bottom of the original upload:

Copyright Disclaimer under Section 107 of the Copyright Act 1976

All rights reserved to the owners the same.

Finding the original upload gives us also a lot more information to go with, from it's description box:

The white man in the video is the film director Jean-Pierre Dutilleux.

The tribe in question is the Toulambis.

The video is allegedly filmed in 1998 (which, again, is false).

Using that information, I was able to find The hunt for authenticity, an article published in the peer-reviewed journal The Journal of Pacific History, in which the author claims the video is fake but not in the way you would expect. To quote the abstract,

Living neither as cavemen nor as colonized subjects, the Ankave-Anga (Papua-New Guinea) are sufficiently isolated for journalists to have seen them as a “lost tribe”, even though their “contact” with the outside world dated from the 1950s. Nonetheless, decades of interactions with the state, church and marketplace have not deeply altered their society. Australian archives and accounts of life “before the white man came”, even though they refute journalistic dreams of authenticity, paradoxically portray places and times that history can hardly explain.

Unfortunately, there is no English version of the article freely available online. There is, however, a French version of the article which can be read here. According to the article, it is apparently largely documented that Jean-Pierre Dutilleux was not the first white man to meet the Toulambis. From the 2004 English translation:

Although they intermarry with the groups from the two other valleys (who are at a distance of one or two days’ walk), are initiated at the same time as them and visit them regularly, they are sufficiently isolated for every European who passes through to feel compelled to take photographs of them. Prior to their appearance in the Stone Age in Paris-Match, they had allowed at least three anthropologists to photograph them: Jadran Mimica in 1979, myself in 1985 and Pascale Bonnemère in 1987. Situated downstream of the trade route that has historically provided the rest of the Ankave tribal group with steel tools ... the Yoye Amara/‘Toulambi’ abandoned their stone adzes at least 50 years ago. ‘At least’, because our informant Idzadze Erauye, who was born around 1945, had never seen any stone adzes in use; or again, because Witi Dzadze, Erwanguye Patse and Idzi Erauye (all about 60 years old in 1990) were very young initiates when the first steel blades arrived. The length of time that has passed since this move ‘from stone to steel’ is confirmed by a patrol officer who crossed the southern part of Ankave territory in August 1950. Though ‘worn almost paper thin’, metal tools were rare and were used communally, but they were well known, particularly to the ‘Toulambi’ who traded them. The Australian colonial archives also indicate that ‘Toulambi’ territory was visited by at least six government patrols between 1929 and 1972:

Interestingly, Jean-Pierre Dutilleux is also cited in the article, defending himself that:

“If the Toulambis are actors, we should give them a César Award.”

In either case, if you are fluent in French and are curious to see the whole documentary, it can be purchased online here for about three euros.