Is it possible that the mentioned hadith is attributed to Hudhayfah instead of Al-Nu'man, and why did Al-Nu'man act in that manner?

There is nothing in the hadith to indicate that Al-Nu'man remained silent. Rather, the questioner asked his father, Bashir ibn Sa'd, and Hudhayfah answered him. Bashir's not speaking does not mean he was afraid. Rather, it was either because he spoke little about the Messenger of Allah out of caution, or perhaps he did not remember the mentioned hadith. It is also possible that he hesitated to speak in the presence of Hudhayfah because Hudhayfah was the most knowledgeable of the Companions regarding hadiths about tribulations.