I'm pretty sure this is their business model rather than an unwanted misconception. FB's growth in the US is slowing so it's to their advantage to monopolize traffic in developing countries.

In fact, considering FB's past attempt in India to offer something leaning heavily toward "Facebook-only Internet"[0], it's more likely a misconception they want to reinforce, not correct.

[0] No source because I'm on my phone and fuck all those AMP links returned by Google. Just look up 'facebook internet.org fiasco'.