This is so because the transmitters had all agreed on one circumstance and delivered the report while they were at lunch.
Likewise, if the narrators are unanimous in employing a specific wording of transmission—such that each one says, “anbaʾanī So-and-so (So-and-so informed me), who said, anbaʾanī So-and-so…,” right to the end of the chain—we would also call this a musalsal, for the transmitters have settled upon a single formula, namely, “anbaʾanī.”
The poet’s words, “A musalsal, say, is any report that comes with a single, recurring trait,” mean that whenever a narration is characterized by one consistent attribute among the transmitters—be that attribute a formula of delivery or the state of the narrator—it is termed musalsal.
His next line, “For instance: ‘Indeed, by Allah, the young man related to me…,’” has already been quoted. In this example every narrator says in turn, “anbaʾanī So-and-so, who said, anbaʾanī So-and-so,” until the chain concludes. This, too, is labelled musalsal because the transmitters concur on one wording in their narration. The same ruling applies if they all adopt the expression “samiʿtu” (I heard), or “qāla” (he said), or anything similar; all such cases are described as musalsal.