The text applies fasaha to three subjects: an individual word, a stretch of discourse, and a speaker or writer. The general concern is related, but the criteria are not identical at all three levels.
SubjectExpression
Individual wordكَلِمَةٌ فَصِيحَةٌ
Discourseكَلَامٌ فَصِيحٌ
Speaker or writerكَاتِبٌ فَصِيحٌ
Calling one word fasih evaluates the word; evaluating a complete expression or its author involves additional considerations.