The total starch method uses the NaOH treatment to expand and loosen the starch allowing more accessibility for the acting enzymes.
Thermostable alpha-amylase is used in the K-TSTA kit to then hydrolyze the resistant starch. This is fine as it is used as a total starch measurement.
If you wish to get accurate measurement of resistant starch you would need to use the K-RAPRS kit as the PAA/AMG used gives accurate measurement of physiologically relevant RS.