Factual error: In the scene where Billy's brother argues with a miner in the local shop, there is a plastic Polo dispenser that wasn't around in 1984.
Factual error: The grown up Billy in the end of the movie has brown eyes where as Jamie Bell's (Billy's) eyes are blue.
Factual error: After Billy dances in the gym in front of his father, he goes out in the cold, everything is covered in snow, but no steam comes out of his mouth...
Answer: Some time has passed since Billy left home and became a professional dancer. Jackie is older now and not as physically active as he once was. He has also seldom left his small, provincial town, and being in a major city like London is a little daunting for him, so he is a little uncomfortable and out-of-place.
raywest
I'd agree with "overwhelmed" (or in awe), but not to the point of being "daunting" because he was eager and excited to see what Billy had become and was not trying to avoid going there. (It was more like he was trying to not let on how excited he actually was).
KeyZOid