Remember Allah's blessing unto you when some folks intended...
3 of his book titled Sirah . Allah has applied the collective plural "people" for this lone man just to express His blessings, the Dear One, the Omnipotent, upon the Muslim masses manifested in the safety of the Prophet, peace be upon him and his progeny. In the Mubahala verse, He has applied both the singular and the plural forms to the "sons," "women," and "selves" to both the Hasanain, Fatima, and ‘Ali in particular, just to honour to their lofty status, may Allah be pleased with them.
Examples for the application of the plural form for the individual wherever necessary are innUmarable and beyond recounting, and they all prove the license to use the plural form while talking about one individual whenever there is a nice eloquent effect thereto.
III Quoting Imam al-Tibrisi, In his interpretation of this verse, in Mujma’ul Bayan fi Tafsir al-Qur'an , Imam al-Tibrisi comments on the usage of the plural form to refer to the Commander of the Faithful as a token of respect and veneration, stating that lexicographers describe the singular using the plural form to show respect and veneration.