Have you considered whether there is an income tax treaty with your client's home country, whether your client was a resident of the treaty country by (usually) Article 4, if there is an article that covers the income in question, and, if so, how and where that income should be taxed, and if the income is taxable in the US, whether that article provides for similar tax treatment as if a US resident?

In the absence of any treaty exemption or concession and provided your client is eligible to be treated as an exempt individual, he/she would be subject to US tax as a nonresident alien (NRA).  NRAs, under the IRC, are not eligible for standard deduction - that's why PS only computes itemized deductions on the 1040NR.

Based on NC's statutes, GS 105-153.3(15) and (11), you client may be considered a nonresident for NC individual income tax purposes.  Although NC does not explicitly require modifications for federal tax treatments for treaty income, your client will still need to file a NC return if he/she meets the relevant thresholds explained in D-401.