There probably aren't 800 billion websites, most likely they are counting individual pages as their own website
If I had my own website, and on it was 2 pages, I bet the Internet Archive would count those 2 separate pages as their own website entirely
Or maybe they're counting the total amount of times every webpage on the internet has been saved on their site
Either way, there's no way there's 800 billion sites. That's such a high number it seems ridiculous. Doing the maths, that would mean every person on Earth would have 100 websites.
EDIT: I searched it up, and apparently there are only about 1 billion websites