We belong to the same cultural region. Even in the early modern era the inhabitants of the Horn, Sudan, Southern Egypt (Lower Nubia) and Chad largely dressed in that white-robes motif:
The Tobe, or Abyssinian “Quarry,” is the general garment of Africa from Zayla to Bornou. In the Somali country it is a cotton sheet eight cubits long, and two breadths sewn together. An article of various uses, like the Highland plaid, it is worn in many ways; sometimes the right arm is bared; in cold weather the whole person is muffled up, and in summer it is allowed to full below the waist. Generally it is passed behind the back, rests upon the left shoulder, is carried forward over the breast, surrounds the body, and ends hanging on the left shoulder, where it displays a gaudy silk fringe of red and yellow. This is the man’s Tobe. The woman’s dress is of similar material, but differently worn: the edges are knotted generally over the right, sometimes over the left shoulder; it is girdled round the waist, below which hangs a lappet, which in cold weather can be brought like a hood over the head. Though highly becoming, and picturesque as the Roman toga, the Somali Tobe is by no means the most decorous of dresses: women in the towns often prefer the Arab costume,—a short-sleeved robe extending to the knee, and a Futah or loin-cloth underneath. -First footsteps in East Africa
I strongly suspect that by its strong resemblance to Ancient Nubian and Egyptian reliefs this style of dressing is thousands of years old and it may have also once been just as common in Arabia as well given the Hajj dress-code and some examples I've seen of Bedouin attire across Arabia around the 19th century.
Sounds more like this is just rural arid/desert wear or bedouin dress code adopted for the climate and lifestyle/economics which the whole region share with eachother, rather than a strict traditional dress code
It's like you said. Bedouin Arabs used to dress the same way. And it's being mimicked through the Umrah clothing today. The same two futah
However, its important to note. The modern tobe or qamis, is just an extension/variation of the bedouin style of clothing, with the difference being that the fabric is sewn/stitched together rather than being open ended and this too was visibly worn throughout the region and most common among the settled communities in the early modern period. In a lot of cases wearing tailored/stitched clothes with elaborate designs, quality fabric like silk and/or colour pattern was an expression of wealth or status.
Examples of this stitched/sewn/tailored clothing/robes worn in 19th-20th century by settled/coastal Somali women from various clans/regions.
This one is wearing what appears to be a blouse called ''Kurdad'' mentioned on this thread:
Traditional somali blouse
Examples of this sewn/stitched/tailored clothing/robes in 19th-20th century worn by coastal/settled Somali men
Inhabitants of coast of Somalia, Africa in 1838
The turban ''Duub'' is a common place among Somalis as it was for Arabs but there is also the shawl/headscarf that they would cover their head with called ''Khayli'' in Somali, modern manifestion of this is seen in the Saudi Shemagh and Palestinian Keffiyeh.
I also mentioned in a different thread about men wearing military pants called ''
Targaal''
Side note: There is also the cloak/Jacket they used to wear, which s feature prominently among the religious and urban elites used to wear throughout 19-20th century. You have an example of it on in your display pic.
What's noteworthy about this and why i bring it up is that it kinda similar to the royal cloak with golden embroiled patterns that Habeshas wear in their weddings and the swahilis wear a similar one but with a different pattern and style.. Maybe points to a regionality same as the Tobe.