When does the second clause function as istiʾnāf bayānī after a merchant hurries back?

Supplementary Practice 17: Market Inspection, Evidential Scope, and Rhetorical Precision

• Only when the second repeats the first verbatim
• When it answers the implied “Why did he return?”
• When it is wholly unrelated and answers no implied question
• When a formal condition is followed by a jussive apodosis