وَقَدْ أَحَاطَتْ بِهِ أَخْلَاطُ الزُّمَرِ
And assorted groups of people had surrounded him.
Akhlāṭ indicates a mixture; zumar is the plural of zumrah, a group. Aḥāṭat bihi means they encircled him.
The audience is not described as a single uniform body. It is a diverse, closely gathered crowd.