If you are not using a FQDN, and NSLookup can't find it but ping can, then it's probably a NetBIOS name being broadcasted by the remote machine and not a DNS entry, HOSTS entry, or anything on the local system, or anything handled by a central server (assuming you don't have a WINS server set up).
You can use
nbtstat -r to get a list of host names that were resolved via NetBIOS (over TCP/IP) broadcasts.
Host name resolution generally uses the following sequence:
- The client checks to see if the name queried is its own.
- The client then searches a local Hosts file, a list of IP address and names stored on the local computer.
- Domain Name System (DNS) servers are queried.
- If the name is still not resolved, NetBIOS name resolution sequence is used as a backup. This order can be changed by configuring
the NetBIOS node type of the client.
Above quote from MS KB172218: Microsoft TCP/IP Host Name Resolution Order