The guys only joined in to give her encouragement but you'll see first Julie than Reggie than Luke notice that the audience can see the band. That's why Julie asked Luke "Is this really happening?"
This was the first time they played together (Julie looked surprised when they pop up on the stage because she doesn’t expect that) and it was the moment they realized that when the phantoms play with julie they can be seen by other people. This is my favorite song from the series and I love your reactions to JATP! (Sorry if I said something wrong, English is not my first language 😂)
She's nervous because it's the first time she's sang in front of anyone since her mom passed and the students are supposed to be heading back to classes but you'll see them stall as she starts.
