Why is “jāʾa al-tilmīdhu wa-huwa lā yatakallamu” not a simple exception for the bare affirmative imperfect?

Supplementary Practice 5: Textual Analysis, Scope of Meaning and Rhetorical Judgment

• The construction is a restriction rather than a report
• Every word is conditional
• It contains no pronoun
• It is a nominal clause with huwa and a negated imperfect