I think they're referring to some early java applet clients that were popular back in the day. he might have telnet'd into the servers that the clients (which were hosted on geocities) would connect to.

only reason why I think that is because I did similar and even found a way to circumvent room bans using telnet 🤣.

In one server variant you could change your name to a mod after they left the room and have admin privileges in that room.

a particularly shitty mod at the time received my ire and I was able to ban them from their own rooms because the software only validated on the clients to not ban yourself 😈

man, I've always been an asshole.

I never had a conversation on geocities, but I do remember you could do some SSI stuff, so maybe it was possible. I think lost my last geocities site password and didn't care to go through the effort of resetting it in '96 or so.

You can telnet into the HTTP port basically everywhere that doesn't auto-redirect to the HTTPS port (and start/resume a TLS session), and there could be stuff in the HTML source (or headers) that a browser might hide from you, at least by default -- but I can't think of how you would use that in geocities to "see private messages". (In theory you could manually start/resume a TLS session, but a proper telnet client might break on some of the bytes received, and you'd definitely have to figure out how to send some non-ASCII bytes.)