Chilli and Beans are two different groups of crops having different nutrient requirement for them to grow well.
Beans is a leguminous crop that can help fix nitrogen back to the soil after the soil nitrogen content has been depleted by crops that use up nitrogen in the soil.
So, one of the possible reasons why Sangay plants Chilli the first, and beans the next year could be to ensure optimal productivity, as beans would replenish the soil with nitrogen. Also, both crops have different nutrient requirement. Nutrient requirement for both crops vary.