But they all have the same UID, and are technically "the same user", even if you foolishly confer disparate usernames and passwords on them. When the system reverse-maps their UID it will display "root" because there is, ultimately, only one superuser on Unix.

The situation is the same for any userid and any groupid. If you try creating three ordinary users with a UID of 3005, they will be, essentially, the same user. There is no way at the system level to differentiate them, after they have authenticated. Because their files and processes are owned by the same UID.

This sharing of UIDs is generally discouraged and quite undesirable. It makes systems administration a real mess.