I think its important for tough competitor's to never ever show signs of weakness, and I'm sure many boxers would agree with that. To that end, there is a point.
acting as if you've won when it's clear to everyone in the building that you lost thoroughly is delusional or perfunctory. Also, I personally believe that showing disappointment over a loss, or at the very least, indifference, is not a sign of weakness in the slightest bit. If anything, it hints at one's passion for victory.