He likely knew that James was an apostle who had been especially close to Jesus.
وَلَا بُدَّ أَنَّهُ عَرَفَ أَنَّ يَعْقُوبَ أَخَا يُوحَنَّا هُوَ رَسُولٌ وَأَنَّهُ كَانَ مُقَرَّبًا جِدًّا مِنْ يَسُوعَ .‏