The basic sense of fasaha is clarity, while the technical category sets more precise conditions. A reader may receive an explanation of difficult wording and understand it, but that explanation does not necessarily remove a defect in the expression itself.
For instance, a word may be extremely unfamiliar to its intended audience. Explaining its meaning may help comprehension while leaving open the question of whether the original diction was technically appropriate.
Thus, comprehending an expression and judging it to be fasih are different claims.