I think the author has become a little confused by what nautical mile means today and has meant in the past.
Originally (maybe as far back as the 15th Century) a nautical mile was just 1 minute of arc of the Earth's circumference no matter where you were on the Earth.
A nautical mile at the pole would be quite short, a nautical mile at the equator would be quite long.
Originally (maybe as far back as the 15th Century) a nautical mile was just 1 minute of arc of the Earth's circumference no matter where you were on the Earth.
A nautical mile at the pole would be quite short, a nautical mile at the equator would be quite long.