Per the link:

Sherrill, a Democrat, said on Tuesday that the MVC error — which lasted from June 2023 until June 2024, predating her own tenure as governor by several years — arose during the application process for driver’s licenses and ID cards. Around 6,600 individuals marked themselves as non-citizens when they applied but were added to voter rolls anyway. The accidental voters were “scattered across the state” and registered under a variety of party labels, according to Sherrill, with the “majority” being unaffiliated voters.