Salt is listed twice - is one supposed to be baking soda?

Yes. The commonly accepted practice in recipe writing is to list the ingredients in the order they are used.

Since the recipe instructions list the baking soda before the salt, it is likely the author meant 1/4 tsp. baking soda and 1/8 tsp. salt. That would be a more logical proportion anyhow since this shortbread needs chemical leavening agent to rise.

Best of luck.