Nathan,
There are a number of things happening with this.
For the Data source, you choose one of the options. In your case, you chose Context, so you don’t need the Microflow that you’ve selected on this page.
Once you select Diary as the context entity, you should be able to navigate to the Calendar item attributes via the association between Diary and CalendarItem. You should have this ability to navigate to these attributes after you click the Select button for each of the event attributes (Title, Start, End, etc.)
Configured this way, you’ll get all of the CalendarItems associated with the Diary object retrieved by microflow DS_DiaryGet.
Hope that helps,
Mike