Publicly announcing that you're negotiating with one faction of the Iranian leadership (who is then implied to be selling out the rest of the Iranian leadership, who will certainly be killed or jailed in the aftermath) and then playing coy about who it is is a great way to sow division among the Iranians, who are already suffering from fractured leadership and the inability to communicate with each other.
It would have been even better if Trump produced some credible evidence of negotiations with parts of Iranian leadership, because then their options would amount to killing each other or waiting to be killed in the infighting.