Hey now. As long as you don't preface your performance by saying "Hey, I'm the next Pavarotti!!!!" you'll be fine.
But seriously - totally different things. I said this in another thread over in Zoo Station, but I would be you any money that the producers told/asked that guy to sing "Nessun Dorma," because they probably all got together and said "Hey, we need to recreate the Paul Potts sensation over in America!"
Which means for those viewers who've heard/seen Paul Potts sing it, you can't help but compare. And Paul Potts sang it far better.