I raised my eyebrow at that comment and found [1] and [2] which mentions evidence of human influence in the region, though I can't watch that BBC doc in my region, the paper is pretty interesting in there appears to be some lost civilization buried under the trees. That paper is from 2003 so I'd imagine there's more up to date research somewhere out there. I'd consider the statement "man-made" to be massively exaggerated unless proven otherwise.

[1] https://www.bbc.co.uk/programmes/b0122njp [2] https://www.semanticscholar.org/paper/Amazonia-1492%3A-Prist...