That comment was in relation to Coleman not being ready to play at fullback. He has been excellent pushing forward, but you can't deny that he has been dodgy at best in defence. He has been extremely lucky not to have conceded a couple of penalties and no doubt the yellow / red cards that probably should have come with the fouls. He'll improve with experience, but he's not a full-back yet.
In relation to that, the one place Ireland has an abundance of talent is on the flanks. Sure, Coleman has played well for a few weeks on the wings in the Premier League, as have many other players who are now plying their trade in the Championship and lower. By the time the next international game rolls around, we'll have a better idea how good he is. I think most people here would agree that he'll ultimately end up as a right sided defender.