Sorry I wasn't being clear!

It's a bit like email. If Lemmy is Yahoo Mail, Piefed might be mailbox.com or whatever. They can talk to each other, but they're not the same platform. So unlike Redditors who are all on the site, the people you'll talk to here are scattered all over a bunch of different websites.

That's why the user names look like emails - mine being @cabbage@piefed.social because I use PieFed.

It doesn't really matter much in practice as a user so I didn't want to get technical about it, but it's part of the reason why you won't see the phrase "lemmings" as much as "redditors". :)