I think he's saying that your statement "I'd gain all of the money for a start" only works if you knew that Nick was going to "split".

Prior to the actual decisions it of course merely one possibility of several - but is enough for there to be a clear reason apart from 'spite' to make the move. The significance of the other-shares outcome actually occurring is in as much as it denies any "stealing is spiteful" advocates the inevitable fallback of claiming that the 'steal could win' options is unrealistic and that the word of the ultimatum guy should be accepted at face value. ie. It is a rejection of the premise of the preceding comment.