Weather can play havoc with pipes, be it cold air or wind, and in cold dry atmospheric conditions a sheepskin bag can prove less airtight than normal. I know many pipers nowadays use goretex bags, but I would expect that a piper of the calibre who would be rostered to play on such a momentous occasion would only be prepared to play the real instrument with a sheepskin bag. It can also be more difficult to seal your mouth airtight over the pipe chanter when your lips are very cold. Compound standing in the cold with the emotional nature of the occasion and it would be a difficult occasion for even the most experienced piper. I'm sure he will be very disappointed indeed at the way the performance turned out and one has to wonder if anyone else could have done better in the particular circumstances.