DataNAV: Please clarify the differences between “Update items” vs “Refresh” vs “Refresh All”

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I manually edited the name of a item that was brought over from an XML Data Source via DataNAV, and also changed a value that was brought over via DataNAV. If I right-click on the Category tile and choose DataNAV->Update Items, I would expect that the item name and value reverts back to the original name (since my XML Data Source remains unchanged). But it doesn’t do anything.
If in the Data Sources panel I right click on my data source and choose “Refresh”, then the item name and value reverts back as expected.
But why does right-clicking on the Data Source name give me options “Refresh” and “Refresh All”, while right clicking on any column within that Data Source only give me “Refresh All”? Seems counter-intuitive (as does “Add Data Source” appearing when right-clicking on a Data Source column).

jlin Selected answer as best March 7, 2019