Other than the NY unemployment income, I did not earn any other income in NYC or NY State in 2018.
Your NY unemployment is NY-source income and thus taxable by NY. As to whether you must file an NY tax return, see "Who Must File" on page 7 of this reference: https://www.tax.ny.gov/pdf/current_forms/it/it203i.pdf
Your NY unemployment is not taxed by NJ. Unlike NY, NJ does not tax unemployment benefits.