Visible crew/equipment: Throughout the film, set equipment such as the boom mic and pole, reflector screen or monitor are visible in the reflections of characters' eyeglasses and sunglasses. Such as when one of the Sharpettes asks, "So what's the theme of the summer's talent show?" in Sharpay's next close-up the boom mic and pole are visible in the reflection of her sunglasses.
Visible crew/equipment: During Fabulous in the beginning of the song if you look into Sharpay's sunglasses you can see a white light reflector.
Visible crew/equipment: After arriving at Lava Springs, when Sharpay signs her initials on the last two fliers in the wideshot, the reflection of the camera and crewmember are reflected on the surface of the Star Dazzle trophy, right beside Ryan's (blue shirt) reflection on its right. (00:11:45)
Answer: It's a Musical. Instruments that aren't shown are always playing like this in these types of movies.