There's no way a city would just close off the channels from boat traffic. It's generally more efficient for hauling goods than land travel, and the second most important reason almost all settlements are close to water.
Also, at least they don't seem to insinuate that everyone in that world is bad at cooking, just that particular party. Still seems like cooking is a somewhat rare skill, when it should be a basic skill for common people, at least as far as basic cooking is concerned.