I assumed these were just the same communities only started on different servers?
This is correct. Anyone can start a community on any Lemmy (Or KBin) server, and they can name it whatever they want. When a community is on a remote Lemmy instance, you see the @<instancename> suffix to help you see which one it is referring to. When no @<instancename> suffix is shown, that means that the community you are looking at is hosted on the instance that you are currently viewing Lemmy content through.