Cold rice noodles are eaten as snacks, not as staple food.
Most of them are young people and most of them are students.
By the way, I am from Beijing. When I went to Shanghai for training in 2005, I really hardly saw anyone selling cold rice noodles. Later, I asked the local people in Shanghai why they didn't see anyone selling cold rice noodles. Shanghai people say there must be, but there are few.
There seems to be a lot of cold rice noodles in the north. For example, in Beijing, especially in summer, most restaurants sell cold rice noodles, which are usually cold dishes.
Thank you ~ ~ ~