Good question. I'm inclined to say typo.
That's what I figured. If the numbers are reversed, it's a 10 point swing towards the GOP in 1980, then another 2 point swing towards the GOP in 1984. Seems just about right.
Although North Dakota as a whole went quite unusually strongly for Reagan in 1980. It had the single largest Republican swing of any state in the nation in 1980 and then the largest Democratic swing in 1984 (excluding DC anyway). So I was wondering if there was something Carter did to really piss off North Dakotans in general and Sioux county in particular. Or did it just exhibit anti-incumbent bias through this period of time?