Amisom is not alone Alpha group are also stationed at the airport along with Turkish boots in fake advisory role, the Turks run the entire security of the Airport so you can rule them out for sure.
You can rule out Ethiopia too it has no business or interest to do so, neither does Turkish Airline which doesn't even go to Hargaisa anyway, FlyDubai is a rival and the Turks control the security of the airport, so you can rule them out too. If it was a bomb it was on-boarded in Jeddah, likely decompression, these aircraft are piss old
1)the most likely option is that is was the mogadishu government. The recent threats to hargeisa, majority of airlines to them to piss off so they took action.