Does it make sense that someone is required to sell both sides of a duplex in NC?

[Tiamo Wright]

I toured a duplex that is a new build and the developer said that he had to sell the units together, that it was required. Any insight on if this is a Charlotte or North Carolina limitation? I wasn't sure if it was just a limitation that he encountered as a developer or if as the new owner I would run into that should I ever need to sell in the future, just want to make sure that I knew more before jumping in.