See row 85 here: https://confluence.hl7.org/pages/resumedraft.action?draftId=44499214&draftShareId=0f85ef1a-c5f3-4292-8829-68185a9b35e9&

As part of the Value Set Definition Profile project, the VSD element DrawnFromCodeSystem.DescriptiveName has been mapped to the extension, valueset-systemName.

The extension description is:  

The human-readable name for the code system.

In FHIR, a human-readable name is the title element.  Rather than change the name of the extension, the workgroup decided to propose the extension text be updated to include

If a CodeSystem resource exists, the value in this extension aligns with CodeSystem.title.