Hi Chris,
When you hooked up the Alteryx metadata loader to your Gallery, it ingested all technical metadata including information about the data sources that fed your workflow. A '0 match' happens when the underlying data source(s) listed under Data Connections have not been loaded into Connect.
Using the server and database information, find the missing data source, setup the appropriate metadata loader and bring it into Connect. Once it's there, Connect will automatically make the match (100) and draw the lineage in Nexus.