It had group chats too, but still, the chat rooms themselves in AOL were ephemeral. No one knew who you were on AOL unless you let it be known, and you could make up a persona if you wanted.

As for word-of-mouth spread at Harvard about Facebook, well that's not different than anything else. Word of mouth is always a part of marketing for any product. You still needed to manually look up your friends or your friend's friends and even to see what was up you'd have to visit their profile (until the feed came out later). Facebook didn't start off by showing you thousands of people you didn't care about, it did the opposite, it wanted you to connect with people you knew IRL.