This method is only useful when the IP address belongs to a server that only hosts few websites. It’s also not very useful if the site is hosted on a shared platform (e.g. Github Pages, Cloudflare Pages, Netlify, WordPress, Blogger, etc.).
But I thought that the subdomain of a website also shows up for ISP, and all the given examples use subdomains not URL to separate websites. i.e: example.github.io instead of github.io/example. In the latter case, ISP can’t know you’re accessing “example” but in the first one can know.
There’s probably just a minimal advantage, I wouldn’t consider it private. The page is discussing IP/website correlation specifically, imagine this:
If you are not using Encrypted DNS, and your ISP only inspects DNS queries and IP traffic,
When you visit site-a.github.io,
Your ISP sees you made a DNS request for site-a.github.io
Your ISP sees you connected to 185.199.108.153 (and knows this IP belongs to GitHub)
When you visit site-b.github.io
Your ISP sees you made a DNS request for site-a.github.io
Your ISP sees you connected to 185.199.108.153
Thus, your ISP can tell when you visit Site A or Site B specifically. But, if you are using encrypted DNS:
When you visit site-a.github.io,
Your ISP can’t see your DNS request
Your ISP sees you connected to 185.199.108.153 (and knows this IP belongs to GitHub)
When you visit site-b.github.io
Your ISP can’t see your DNS request
Your ISP sees you connected to 185.199.108.153
Thus, your ISP can’t tell when you visit Site A or Site B specifically, just that you visited some site hosted by GitHub on that IP.
But, we don’t live in a perfect world, and as you pointed out, SNI (and OCSP) also leak the domain you’re visiting. So realistically yes, there isn’t much of a privacy advantage to visiting sites on shared hosting.