You dna nerds are to blame for cringey displays like this
Habeshas don't have large foreign Bantu populations occupying their best agricultural land. Somalia is largely a desert/semi-arid with the small strip of fertility being occupied by a foreign nation. This is bound to cause tensions.
Secondly, the AU headquarters are located in Ethiopia and Ethiopian schooling/media inculcates them with pan-Africanism. They also feel some pride in that their tricolour was copied by other African nations. Somalis are not under any of that propaganda and largely don't believe in pan-Africanism.
Lastly, at the time of writing, most of Sub-Saharan Africa is Christian rather than Muslim and Habeshas will naturally feel more kinship towards Christian Africans.