Determine how much income is derived from his work in NC. If you own a business based in NC and it creates all the income, then it is all NC income. If instead, for example, half the work is done at home and half in NC, then you can split. Make a note of how you determined your numbers and keep it with your tax records, in case NC asks.
NC instructions state: "If you were not a resident of North Carolina at any time during the tax year 2024 but you received income in 2024 from North Carolina sources that was attributable to the ownership of any interest in real or tangible personal property in North Carolina, derived from a business, trade, profession, or occupation carried on in North Carolina..."