This is one of three counties with a life expectancy of “100+.” Out of these three, it is also the one with the largest error margin. If I am interpreting this correctly, the list compilers are 95% confident that the life expectancy of this county is between 67.9 and 100+.
This is most likely due to the relatively small number of people in the county. This is not uncommon in these rankings: of the top 16 counties in life expectancy, the highest population is over 55,000 and several counties have fewer people than the one ranking #1. When there are fewer cases (residents, for this analysis) to consider, it is harder to be confident in the calculated life expectancy. My guess is that this county had the highest expected life expectancy in the statistical model so even with the large confidence interval it ended up at the top of the list.
With fewer people in a number of these counties, the year-to-year predictions could shift more given conditions. Does this mean the rankings should be disregarded? Not necessarily but the confidence interval does provide insight into how the life spans of a small number of residents can change these rankings.