"When their brother Noah said to them," meaning their brother in lineage, not their brother in religion.
﴿إِذْ قَالَ لَهُمْ أَخُوهُمْ نُوحٌ﴾ أَخُوهُمْ فِي النَّسَبِ، وَلَيْسَ بِأَخِيهِمْ فِي الدّين.
