You are reading a tafsir for the group of verses 18:89 to 18:91
ثم اتبع سببا ٨٩ حتى اذا بلغ مطلع الشمس وجدها تطلع على قوم لم نجعل لهم من دونها سترا ٩٠ كذالك وقد احطنا بما لديه خبرا ٩١
ثُمَّ أَتْبَعَ سَبَبًا ٨٩ حَتَّىٰٓ إِذَا بَلَغَ مَطْلِعَ ٱلشَّمْسِ وَجَدَهَا تَطْلُعُ عَلَىٰ قَوْمٍۢ لَّمْ نَجْعَل لَّهُم مِّن دُونِهَا سِتْرًۭا ٩٠ كَذَٰلِكَ وَقَدْ أَحَطْنَا بِمَا لَدَيْهِ خُبْرًۭا ٩١
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3

Dhu’l-Qarnayn’s next expedition was towards the east of Iran. He reached a place where a most uncivilised people were living. The description that there was no barrier (shelter) between them and the sun means perhaps that they were nomads and were living on open ground instead of in properly constructed houses.