It was a well circulated rumour at the time so presumably there's some degree of truth to it, particularly considering recent events. Walking out while the side is at a low ebb out of no reason other than personal frustration at not getting game time would have been a million times worse than what Roy Keane did, it'd surely have been the end of his international career under any manager, that action would have been crossing a point of no return without a doubt. You'd have to wonder what his teammates thought of him when it got to them that he was considering such a move, wouldn't surprise me if he wasn't the most popular person in the camp given what we hear about him.
But the fact that he was even considering such an action either means he was content to end his Irish career or that he isn't too bright and just reacts without consideration of the consequences.