Perhaps you could post the actual detection and installation events from the WindowsUpdate.log on this PC, so that we could see exactly what is being recorded with respect to this update. Also, if you could identify the exact "SQL Express" update you're referring to, that would help. Finally, if you could identify all installed instances of SQL Server on that PC (best way to do this is inventory services.msc for configured instances of SQL Server under MSSQLSERVER) that would also help.
Lawrence Garvin, M.S., MCITP:EA, MCDBA
Principal/CTO, Onsite Technology Solutions, Houston, Texas
Microsoft MVP - Software Distribution (2005-2009)