الْمَقَالَ كَتَبَ خَالِدٌ.
The article was what Khalid wrote.
مَا كَتَبَ خَالِدٌ إِلَّا الْمَقَالَ.
Khalid wrote nothing except the article.
The first fronts the object for prominence, whereas the second explicitly excludes other objects of Khalid's writing within the relevant context. These are not freely interchangeable: one highlights an object, and the other denies alternatives.
A plain answer such as “Khalid wrote the article” may fully satisfy “Who wrote the article?” Do not assume that fronting invariably carries the same exhaustive force as negation and exception.