Not all residents of Musaia are demons transformed by the heat of the nether. Originally wanderers of the desert biome, Some joined them intentionally for protection so they could trade the wealth of the nether with others. They obtained purple silk and gold through their trades which helped them develop their distinctive outfit.

Credit to this skin for being the original outfit base:
https://www.minecraftskins.com/skin/21380783/eygptian-outfit-base--steve-model-/