I get what the author's saying -- that white rice is pure carbohydrates, while sweet potatoes are a healthier mix -- but it's phrased pretty strangely. What exactly is rice, if not a plant?
Isn't glycemic index (GI) an important measure of the potential negative effect of the carbohydrate? Some varieties of rice have a surprisingly high GI. Jasmine rice, for example, has a higher GI than pure glucose, a sad fact for me since it's the favorite rice where I live. Other types of rice have much lower GI.
When it comes to sweet potato versus rice, cooking method makes a big difference in GI: Jasime rice = 109, baked sweet potato = 94, boiled sweet potato = 44 [1]
>much of it from plant-based material like the Japanese sweet potato, their staple food, in contrast with the rice-heavy cuisine of the mainland.