I don't think it's unspecified, it's to keep weeds away. Using weed killing chemicals to kill off any plants in your field apart from the specially-weed-killer-resistant crops is super common in agriculture, and is terrible for the environment.
You seem to be against the idea of growing rice in flooded fields, can I ask why? It's not like this is in some places like California that's in constant drought.
Yeah, I think their point is that if China suddenly threatened to cut off all trade with the US, we would be screwed because we no longer have the means to produce everything we need as a nation.