Even though he could have phrased things in a more sensitive way, or even better, said "no comment", I think that Brian's reaction is an example of how affected he will be by Stephane's departure.
Based on my observations, Brian seems to rely strongly on a presense of a 'rival' in order to keep competing at the top of his game. A rival fires him up. Remember when Brian had a meltdown at Moscow worlds? There has been a suggesting that this was a result of Plushenko's withdrawal. He was his main rival at the time, and when he was suddenly out of the competition, Brian was at a loss and we all saw how that turned out.
Brian has been calling Lambiel his main rival since Evgeni left. Even last year, despite the fact that based on the season's results up to that point Takahashi and even Weir had better outings than Lambiel, Brian named only Lambiel as his competition, and only when he was called on the fact that Daisuke has been kicking *** all season, he begrudgingly added him to the list of contenders.
The fact that Stephane is gone will affect Brian the most out of everyone. I think this is a huge blow to his mental game, and his reaction is a reflection of that.