They call them sorts not kinds :-) "Sort" comes from many-sorted logic where the sort distinction is at the syntactic level, so easily inferred. They are not

They call them sorts not kinds :-) "Sort" comes from many-sorted logic where the sort distinction is at the syntactic level, so easily inferred. They are not called "types" because they don't come from type theory; there is no logical richness to the relationships between different sorts, unlike the relationships between types. They are not called "kinds" because that is the name of a higher-order concept in type theory.