Is it possible to find the owner of a GitHub Pages site that is connected to a custom domain?

Is it possible to find the owner of a GitHub Pages site that is connected to a custom domain?

I am curious whether someone could find out if a site hosted on GitHub Pages could be traced back to the user that published it. This is of course, assuming that:

• the GitHub repository containing the website’s file is private,
• the website is connected to a custom domain (using something like a CNAME record, rather than a redirect from example.com to user.github.io/secret-site),
• the GitHub account itself isn’t compromised.