Why was the expulsion of Banu al-Nadir referred to as "the first gathering" (awwal al-hashr) in Surat al-Hashr, when Banu Qaynuqa' were expelled from Medina before them?

There is disagreement regarding the meaning of "first gathering" (awwal al-hashr) in Allah's Almighty saying: (He it is Who drove out the disbelievers of the People of the Scripture from their homes at the first gathering). Some said it refers to the expulsion of Banu al-Nadir to Khaybar, and then their expulsion from Khaybar to Sham. Others said it refers to the first expulsion that befell Banu al-Nadir, as no expulsion had befallen them before it. And it was also said that it refers to the gathering to the land of Sham, which is the land of gathering on the Day of Resurrection. The verse can accommodate all these meanings.