It does seem strange unless Ciro and the other coaches ALL feel that Ariuado isn't yet ready for our first team, even its fringes...which would be a horrifying indication of his complete lack of technique and competency, because our current centrebacks are loathsome. I am excluding Chiellini as he is injured...Perhaps we are trying to grab a right back, and Caceres will be able to move into the centre. But that also seems strange, as he has just started to look fleetingly useful on the right flank.
Still, looking at it in the best possible light. he goes to cagliari, gets games, shows his steel, and has a call back option. Later on in the season, Legro gets shot, and cannavaro dies of old age...and we are forced to recall him, and before the last game of the season, Chiellini and Ariuado show the league that they are set to be a force to be reckoned with, and the future looks ever so much brighter then, than it does now.