In the midst of chaos, a terrifying report reaches King David, claiming that all of his sons have been killed. Stepping forward to calm the devastated king, Jonadab son of Shimeah attempts to dispel the panic. He urges David not to take the alarming news to heart, clarifying that the rumor of a mass slaughter is entirely false [מצודת דוד].
Although Jonadab had previously explained that Absalom only intended to harm Amnon, David still had valid reasons to be afraid. The king could easily imagine a scenario where the other brothers tried to defend Amnon, sparking a violent brawl that resulted in all of their deaths. To put this specific fear to rest, Jonadab firmly assures David that no such battle took place and the other brothers did not die in a struggle [מלבי"ם]. He confirms that only Amnon was killed.
This interaction highlights Jonadab's sharp and cunning nature. He accurately reports the facts of the tragedy to the king, yet he carefully conceals his own earlier involvement in the chain of events that made the murder possible [ביאור שטיינזלץ].