I think the NJ Non-resident tax instruction booklet is a bit clearer:
"If both you and your spouse were nonresidents for the entire tax year, and only one of you had income from New Jersey sources, that spouse can file a separate New Jersey return even if a joint federal return was filed. The spouse with income from New Jersey sources calculates income and exemptions as if a federal married, filing separate return had been filed. You have the option of filing a joint return, but in that case, your joint income would be reported in column A of Form NJ-1040NR."
https://www.state.nj.us/treasury/taxation/pdf/current/1040nri.pdf
If the spouse with NJ income chooses to file separately, only that spouse has to file an NJ return.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
