He couldn't help but tear up a little when he sang that song - it was his second favorite song of all time - and he didn't notice anyone around due to playing with his eyes closed again. He usually did, not able to help it. It was partly that he got into his music too much, as well as part nerves. He wasn't entirely confident in his talents.
But when the song ended and he did open his eyes, he couldn't help but grin when he saw Annie standing there. "I was waiting to see you!"