What affirmative explanation of «fa-laysa minnā» does al-Nawawī report from the scholars in this context?

Reports of ʿAmr ibn ʿUbayd: Attribution, Conflicting Accounts and Evidence of Criticism

• The person has departed from the Prophet’s guidance, knowledge, practice and conduct; this does not necessarily establish takfīr
• Every grave sinner is, without exception, declared an unbeliever and apostate
• It means the hadith is unauthenticated through every route
• It merely establishes that a narrator met his teacher