Revealing mistake: When Troy crouches down on the rocks, and leans down to see his reflection in the water, oddly the reflection is not reversed, yet his hair is combed the opposite way. (Did the director actually think that if Troy's hair was combed the opposite way it would pass as a reversed reflection?) Additionally, when he crouches down, the bottom button on Troy's shirt is unbuttoned, but in the reflection (as well as in the previous and following shots) the bottom button is buttoned up.
Revealing mistake: After Ryan is given the Star Trophy at the talent show, the classmates gather outside holding lanterns. The line pulling Troy's lantern up is visible, just as the first blue fireworks starburst explodes above it. (01:44:10)
Answer: It's a Musical. Instruments that aren't shown are always playing like this in these types of movies.