This discourse arrangement is called resumption (استئناف). The later clause begins syntactically afresh, yet it answers a question that the earlier clause has already provoked. It creates continuity in meaning without requiring grammatical coordination.
First sentence: “The traveller returned.”
Question arising in the mind: “Why so soon?”
Second sentence: “The road was closed.”
These lines are an illustrative teaching example. The question is implicit; it need not be spoken. The final sentence may follow without wāw because its function is to answer rather than to coordinate.