He seems to display all the outward signs of a boy who gets the mickey taken out of him for being keen on singing sacred/spiritual music. He gave an immediate, simple and honest answer to Simon Cowell's "do you get support from your friends?" question, and I guess it was his (very brave) way of saying to his bullies, 'f___ you all, look at me, I'm on the telly'. The interview comments look as though they were gleaned afterwards as a reaction to what was a very small comment, and then cut into the 'pre-performance' part of the broadcast. I think this would have been the producers' idea - these things make good telly. I think his reaction afterwards was out of genuine shyness and nerves. I also think his Mum may well have been aware of both his talent and his bullying and that this is why she supported him on this show.
Anyone who watched 'The Choir' a few weeks ago will understand how modern boys resent singing to the point of hatred of anyone who confesses to it. Hardly any of the boys in that school were prepared, initially, to give it a go, many of them because they would have lost face in front of their 'friends' for doing so - including the son of a very well-known musician.
When you get zero support (and positive ridicule) for something you're even a little bit good at, you begin to learn that there's no point showing emotion, because it doesn't help. Often, it makes things worse.
I would say he is genuine, but I would also say the programme makers are milking it.