In this case, I don’t think there is a gateway involved at all. I believe Let’s encrypt is verifying the authors domains by (essentially) querying their selected DNS provider to prove ownership over a domain, which resolved to a private IP.
So iiuc there is no split horizon, it’s just that the sites would only work for the author.
So iiuc there is no split horizon, it’s just that the sites would only work for the author.