Here is the original announcement for Seafile Drive client. It might provide some insight on what motivated its development and the key differences with the (traditional) Sync client.
The new Seafile Drive Client is the second client for the sync & share solution Seafile. This client makes Seafile the better alternative to the traditional network shares offering file download on-demand, no network delay when browsing files, automatic server sync of file updates and file caching for offline access.