Such a claim has no real basis. Imagine a group intent on frightening the public: they announce, for example, that a shell has fallen in a certain spot, yet they offer no description. Others repeat the same allegation, and so it spreads. Perhaps their sole purpose is to sow panic, and in doing so they lie. By contrast, if people were to bring us an account replete with spoken and enacted particulars, it would be remote indeed to suppose that all of it was fabricated—unless we learned that they had agreed or conspired beforehand.
This, in sum, is what the author—may Allah have mercy on him—wants to establish. His aim is to show that when mursal reports arrive through several independent chains and no collusion or prior coordination can be detected, they are deemed sound: each narrator relates the report from the Messenger, peace be upon him, and their convergence through diverse routes indicates that the report must have an origin with the Prophet ﷺ. Custom tells us it is highly improbable that all of them would attribute it to him without first receiving it through a traced chain.
Note, too, that the author repeatedly appeals to custom. As Ibn Ḥajar observed, matters of transmitted reports are not open to pure rational speculation. Were we to entertain every conceivable intellectual doubt, no report would remain credible and no ruling could be confirmed, for in debate anyone can float a possibility and claim, “It might be such-and-such.”
Nevertheless, this method cannot guarantee the exact wording or the fine details that are unknown through it; securing such precision requires a stronger route, one capable of definitively establishing those very words and nuances.