Does the stomach have thicker walls than small intestine in a frog?

Yes.

The main function of the stomach is the mechanical digestion of food, while the primary role of the small intestine is the absorption of nutrients. The muscular wall of the stomach enables it to churn the ingested food, facilitating the mechanical breakdown. On the other hand, the small intestine does not require extensive muscular activity for nutrient absorption, therefore its walls can be thinner.