The informant is recounting a Chinese proverb from home. He does not remember where he heard it.

“If you grow the watermelon, you will get the watermelon. If you grow the pea, you will get the pea.”

The informant says that this emphasizes the natural causal relationship of the universe.

I see the phrase as being  akin to the phrase “you asked for it” meaning that you shouldn’t be surprised by the result you get when you made designs on achieving that result.