Is the Hadith of Al-Suddi regarding Salman Al-Farisi's people authentic, and can it be understood from it that the Prophet (peace be upon him) might err in determining the destiny of a person in Paradise or Hell?

The Messenger, peace and blessings be upon him, does not speak out of his own desire, and what he says is a revelation from Allah, or an ijtihad (independent reasoning) that the revelation has approved or corrected. If there was an ijtihad from him and he erred, the revelation would descend to rectify and correct it.

The mentioned narration about Salman's companions is weak and断开 (disconnected). The correct view is that the verse was revealed to explain the condition of Salman's companions without the Prophet, peace and blessings be upon him, condemning them to hellfire. The verse is general, encompassing anyone who possessed the described qualities before the advent of the Messenger, peace and blessings be upon him.