The title says it all. See for example the OPs here:
Gnome 3 Shell - Launcher displayed in center of the screen
How can I lock AND blank the screen from the keyboard in 14.04?
Are they the same? It seems to me that we have two different @Seth here.
I imagine it is "working as designed", but does anyone know the rationale behind this? Or what is happening here?
The transactional database doesn't care about some arbitrary nickname but id's. As you have (I presume) noticed, everything has an ID in Stack Exchange, posts, tags, revisions, and users. So, your nickname is linked to a specific ID in the database and that's shared in all the network. So, to answer your question, yes, there can be two users with the same nickname.
Trivia: Once we had two somewhat old users called Private, today's don.joey and Private. They had a charming conversation somewhere in meta.
Remember, quite a lot of people would like to put their own name or a common or popular name as their nickname - a good example being 'Alex':
A previous example of repeated names used to be blade19899 - see here - a lot of which seemed to be copying this user, even the avatar/logo as well:
Also, being able to put the same name means you don't get what you get with many other sites - Alex01, Alex-2, etc - which can if anything be more confusing...
