Who funded this story? It is not humidity alone that determines thermal comfort, but rather the capacity of local infrastructures to manage it.
Follow the incentive: travel guides seek simplicity and generalization to be "useful", but who does this really benefit?
A guide that ignores access to air conditioning sells an incomplete, even misleading, image, since the conflict of interest between commercial simplification and on-the-ground reality is obvious.
For example, comfort in Singapore with its ubiquitous air conditioning is very different from a tent trip in the Amazon, even with similar humidity levels.