For a while now, the Korowai people of Western Papua have been the go-to primitive tribe for documentary-makers. The Korowai were unknown to the outside world until the 1970s — but they’ve certainly made up for it since, with their Stone Age tools, jungle treehouses and penis gourds becoming almost as familiar to TV viewers as Brian Cox on top of a mountain.

No wonder, then, that Will Millard’s introduction to My Year with the Tribe (BBC2, Sunday) smacked of mild desperation as he sought to distinguish his new series from its many predecessors. (No fixers laying on anything in advance! Not just one snapshot of Korowai life, but four over 12 months!) In the event, however, he needn’t have worried. Although he clearly set off with the customary aim of presenting the Korowai as a last, precarious remnant of our hunter-gatherer past, what he discovered instead was far stranger and more surprising than that.

At first, everything went pretty much as you’d imagine. Millard and his crew pitched up in Mabul, a village on the edge of Korowai territory, and inquired where the more traditional tribal members could be found. They then loaded several small boys with heavy kit and began macheteing through the jungle while Millard commented wonderingly on how people could live in such isolation. A few hours later, he’d arrived at a treehouse where a penis gourd-wearer called Markus proudly showed off his naked family and fine collection of pigs’ teeth. He also agreed to take Millard on a hunting expedition — although, somewhat anti-climatically, in search of insect grubs.

Only later that evening did we get the first sign that not everything was as it seemed when Markus’s family demonstrated an unexpected knowledge of how Millard’s smartphone worked. The second came the following day, as Markus led a two-hour jungle trek to meet his nearest neighbours, and at one point stopped to chop theatrically at a tree with his rudimentary axe. Asked by Millard why he was doing that, he looked distinctly puzzled by the need for the question. ‘For the filming,’ he replied, in the patient tone of a man explaining something obvious to a good-hearted simpleton.

Even so, the penny didn’t really drop until the two men reached their destination, where another Korowai family were sitting naked in a treehouse. Initially, these neighbours gamely tried to pretend this was how they passed an average day. But once they realised that this particular day might go unpaid, the truth started to emerge. ‘This is not our home,’ pointed out a family member. ‘These houses were commissioned by Canadians for filming.’ ‘I was told we should be here with our clothes off,’ added one of the two wives.

Her husband, meanwhile, helpfully laid out the business plan of which this was a crucial part. ‘I lie around until there are guests,’ he told Millard. ‘And then I get naked and they photograph me.’ He also provided a handy price list, ranging from £5 for a basic photo to £50 for the full insect-grub hunt.

And with that, Markus also broke the fourth wall, admitting that he lived in Mabul but had come to the jungle when he heard that Millard was the latest westerner keen to see the authentic Korowai way of life. ‘If you’ve enjoyed being here,’ he unambiguously went on, ‘you pay me well.’

Faced with the awkward fact that he was in something between a Potemkin village and a theme park, Millard reacted with an understandable mix of gloom, embarrassment and existential crisis. Not only did he now realise that the Korowai have built an economy on ‘selling brand Korowai to rich tourists and TV crews’, but he also acknowledged that this was because of people like him. ‘Look around you, mate,’ he told himself in one especially bitter moment. ‘You made this.’

And yet, my guess is that not many viewers will have shared his disappointment at the way the programme turned out. After all, which would you rather have? Another plod through the standard stuff or the jaw-dropping revelation that the phenomenon of savvy locals faking their own culture for tourist money has now spread to the remotest parts of the Earth.

With two programmes still to come, I’ve no idea where My Year with the Tribe goes from here: Millard is continuing to plunge ever deeper into the jungle in the quest for traditional Korowai, but so far all he’s really established is the power that denial can exert. Either way, though, Sunday’s episode wasn’t just startling in itself (not least because it took the unusual step of allowing its findings to emerge naturally rather than advertising them at the beginning). It was also a rare example of a TV documentary that proved a lot more interesting than it intended to be.