No, what prompted Ethiopia to wage war was the declaration of war against them by the Islamderthals.
The Ethiopians believed their enemy meant it, so responded in the only manner Islamderthals understand.
There are parts of eastern Ethiopia, the Ogaden region, that have a large number of Somalis. They've been a cause of trouble before, and would be again, were a hostile and organized government rise in Somalia. Rather than wait for the Islamists to consolodate power, they simply took the fight to them first.