I think it's just the computer addressing whoever is there, I don't think it's specifically you. Maybe when Dinklebot hacked the door he triggered Dr. Shim's access code, so the computer thinks you're him. If you'd like to pull out your tin foil hat, we can get into speculation. There's a theory that the entire game world is nothing more than a Vex simulation, run by a Vex specimen that Dr. Shim was experimenting with pre-collapse. So the computer addresses you as Shim because that's the only point of reference the Vex mind has for someone entering the Archive. Pretty shaky theory, and I don't subscribe to it myself, but there it is.