The author seems to be drawing a parallel between udon and soba, but instead of saying they're both Japanese, says that China and Japan are both in Asia. It's somewhat of a non-sequitur that only makes sense if (1) the author thought that udon is Chinese and soba is Japanese, or (2) the author didn't realize that the second phrase would not be read as a separate example but still in the context of "In this case ..." which set up the udon example.
Edit: Looking at the authors' names -- Ferras Hamad, Isaac Liu and Xian Xing Zhang -- I'm guessing the 2nd is what happened. Somehow I get the sense that Xian Xing Zhang and Isaac Liu know where udon comes from.
Edit: Looking at the authors' names -- Ferras Hamad, Isaac Liu and Xian Xing Zhang -- I'm guessing the 2nd is what happened. Somehow I get the sense that Xian Xing Zhang and Isaac Liu know where udon comes from.