According to Table Calculation Types - Tableau
Add Secondary Calculation
With Running Total and Moving Calculation table calculations, you have the option to transform values twice to obtain the result you want—that is, to add a secondary table calculation on top of the primary table calculation. For example, you could add an initial table calculation to calculate the running total for sales per month within each individual year, and then a secondary calculation to calculate the year-over-year percent difference for each month from one year to the next.
You are using the table calculation to get moving sum, but it's not using Tableau's "Moving Calculation".