Chinese love seafood and fish, they consume quite a bit of it as hinted by the article. But they usually also want to buy it alive.
Therefore in supermarkets and even restaurants you usually have tanks with live fish, crabs, etc. As fresh food as can be.
Regarding vegetables, the north is actually not that north by European standards and is sunny in winter (Beijing is at the same latitude as Ibiza...). This means that in places like Beijing they can have solar greenhouses that can produce fresh, local vegetables all year long even when it's freezing outside (winters are much colder than in Europe).
See for example: https://www.lowtechmagazine.com/2015/12/reinventing-the-gree...