pts/2 is the second pseudo-terminal. It can be used for remote shell's (and some kde programs), and console windows in your graphical environment, because they also "connect remotely" (they aren't real terminals, like the framebuffer consoles / serial lines you'll find at screen 1-6).
I'm wondering what other details you have about the unexpected user, and what is the full output of "who" and "finger"?. (please post it here)
I'm wondering whether your machine might be compromised. Programs usually get replaced / dates reset / logs by altered to hide the appearance of another user. Install a rootkit to check your system (don't use your current rootkit, reinstall it)