Thanks for contacting Syncfusion forums.
Query: “My issue is that the filter is showing the values of DocumentId (numeric) vs the display values from the Template definition”
Data operations like filtering, grouping, sorting, CRUD will take place based on the Field property value. Since you have defined Field property with DocumentId, filtering values will be based on the that column only. From your code example, we suspect that you want to display value from another table similar to foreign key behavior.
If yes, we have provided support for ForeignKey Column, where we display text and in the backend we will process the values. Refer the below UG documentation for your reference
If above solution does not resolve your query, kindly get back to us with more details about your requirement.