Well, the create date of tempdb is September 7, 2011 and of the five indexes that don't have any user seeks/scans/lookups 4 of them don't have any system scans/lookups either.

The table I'm looking at is a replicated table on the subscriber side of transactional replication. I'm guessing that those four existed on the publication side and are used there (confirmed just now for several of them) and that whoever set up replication just scripted out the table for the subscriber DB.