No one including my wife was interested in seeing it so I went by myself. It was long, but interesting. The author hits the nail on the head:

“You sit there believing you’re watching a documentary about a woman who deceived the world, only to discover that you’re also watching a demonstration of how easy it is to deceive you.”

I couldn’t agree more.

I haven't seen the documentary, but I have a background in media and art. There are a couple of ways I could understand this.

The first is the general public's lack of understanding of documentaries as an art form. Documentaries are essentially narratives presented as unfiltered reality ("facts"). Most folks don't truly understand this, or they lose sight of it through suspension of disbelief. That is, they don't know or forget about the film crew, editing, framing, and other artistic choices that form what they see. The illusion becomes invisible; they see only "facts" rather than a constructed narrative designed to guide their interpretation.

Second, filmmakers often use deception as an artistic device in documentaries. Mockumentaries are a pretty clear example of subverting the conventions of documentary filmmaking. It's a bit meta for most folks, so I could see how someone without much media literacy might totally miss this. But it's definitely a very interesting artistic choice given the subject matter.

What was deceitful about it?