This is the snob effect. People like the author believe produce is cheaper because of poor quality. Does Chinatown respond by lowering prices further because people won't buy poor quality produce? If it weren't for prejudice then Chinatown groceries might price for more profit. The customers are missing out too. Marketing can fix this.
For instance, it's summer in the northern hemisphere right now. You can't turn around without running into a ripe stonefruit (peach, plum, apricot).
Because the local trees are bearing right now, not only do you get high quality produce, but you get it for cheap because there's a glut of supply. But if you want an orange, you settle for an expensive, tasteless orange flown in from Chile, cause it's winter down there and that's when oranges become ripe.
If you tried increasing prices of produce in Chinatown, people would laugh in your face and move on down. The Chinese culture is very food aware and value conscious.