What you're seeing is the cached credentials. In the event there is no domain controller available, you can still login to Windows using the cached account.
The data you're looking for can be had from the Registry, but you need to implement a little searching to get it. Look under the key
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Group Policy\State\
In there, you'll find a set of keys with SID's for names. Search each folder for a value called "Distiguished-Name" (I think - from memory!) You'll get back an ADS path that you'll have to parse up to get the name.