I'm pretty sure "More difficult" here is a comparison of vectors in a non-Euclidean space of high dimensionality. Depending on how you measure across those dime

I'm pretty sure "More difficult" here is a comparison of vectors in a non-Euclidean space of high dimensionality. Depending on how you measure across those dimensions you can come up with wildly different answers. The author has explained some of how they assess the dimensions.