That's a shared database lock. Each and every running query, no matter what it's running, takes a shared database lock to ensure that the database can't be dropped while the query's running.
You can run updates with that lock there because the lock is not on a table, page or row, it's just a shared database lock.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability