Sorry perhaps a reading failure on my part.
Now that I look at the readme, it sounds like “distance” is probably a straight-line distance in 3D. Is this what you want?
They say "Future work may focus on geodesics and related calculations " which is what I was aiming for. But the package is more sophisticated than assuming the world is a sphere, and thus working out the accurate great-circle distance (i.e. geodesic length) accurately would be harder work.