check out this KB. it has your answer and bunch of other questions answered:
KA312026 - FAQ: BBSA Windows Patch Analysis, Deployment, Troubleshooting
if no access to KB, here is the snippet:
- Looking through the Analysis Results, you can see the Severity column. This column will provide the severity level of Security Patches only, and for rest of the patches, including Service Packs it will be listed as 'Unknown'.
So, all non security related patches are listed as unknown then?
That is correct, and all Security Patches report the severity.