I don't know what's unclear. Nduja used to be unseen outside of Calabria. Then the American version was made and it got really popular. Now it's seen all over Italy. Those things could plausibly be unrelated, but probably not.

Worth noting that my view here was informed by listening to Italian chefs and salumi experts. Except they just present it as fact while I hedge with "probablies."

None of this should be in any way contentious. More reddit with sticks up butts for no reason.