三野王 was in Tsukushi province with his father who maintained neutrality, where he was in the Jinshin war was far away from where 美濃王 was, that's why 美濃王 and 三野王 were obviously different people.
三野王は中立を保つ父とともに筑紫国にあり、距離が離れ態度が異なるので美濃王とは明らかに別人である。