Eating afterwards may enhance the effect of the kratom
due to gastric emptying, the same way drinking beer after spirits causes an enhanced effect of the spirits (often resulting in extreme intoxication, sickness..etc.). The more dense substance (food in this case) causes the stomach to begin emptying, and the intestines to increase peristalsis, resulting in a "pushing down" of the previously ingested substance (in this case, kratom). There is probably a fine line between this increase in digestion rate and overwhelming the kratom with too much food.
Furthermore, a little bit of food might help to ease some of the gastric discomfort that some people experience with kratom.