One student attributes an article to Amr; another replies:
مَا كَتَبَ الْمَقَالَ إِلَّا خَالِدٌ.
No one except Khalid wrote the article.
The dispute concerns authorship, not whether the article was written. “Khalid wrote the article” supplies a competing claim; the restrictive form explicitly excludes the rival attribution. Within this dialogue it functions as qaṣr al-qalb, reversing the listener's false belief.
Emphasis on an event and restriction of its agent are thus distinct rhetorical operations.