You're correct that a worker residing in NJ but working in NY State needs to file both NJ and NY State income tax returns. But the person you are responding to stated that such a worker needs to file and pay NY City income taxes, which is incorrect. In addition, you're not entirely correct when you say that this worker won't have to "pay both" - it's common that such a worker may owe money to both states, either because the worker has some NJ-only income (e.g., checking account interest) or because the NJ tax credit and the tax systems of the two states don't line up exactly right.