That is the artwork of the kingdom of Makuria, Faras, Nobatia among others, again before the majority of the population became islamic.
Prior to the Europeans coming to that region, which they separated both Northern Sudanese and Egyptian from going until the 1950's Egypt and Sudan was one country. The majority of the Southerners were living like this, and some still do to a certain degree. Before the British they did not have a writing system. Also to note the "gods" they worshiped were nearly Monotheistic in nature. In other words, they did not worship Amun Ra, Isis, nor Apedemak. Did they suddenly abandon it all, and have a fresh start.
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Now i am not mocking their culture which i think is beautiful and unique, but at the same time you need to ask yourself these questions.
Now compare from the artwork before
Present.
Weirdly we play similar instruments.