It is a sidetrack about whether boundaries are sharp. That they are not sharp is illustrated by the Schrödinger’s cat thought experiment.
I think I was clear enough about my point, when I said:
Obviously, people disagree, but seem unable to explain why they disagree.
Perhaps somebody would care to define “natural category”. I won’t attempt that, since I don’t think they could exist. From my point of view, a category is an abstraction. And I don’t see how abstractions could be considered part of nature.