Just to clarify: the actual number of restaurants and stores tested was tiny. They tested samples from 4 restaurants and 10 grocery stores in New York City.
It certainly suggests that there is a problem with mislabeling, so it is worth paying attention and the issue is serious (some of the fish were swapped for more expensive varieties; others were overfished species that some diners try to avoid, etc.). But the Reuters line makes it sound as if there was some sort of comprehensive, thorough test of many or all NYC restaurants. There wasn't.