And... I'm out. My disbelief is no longer willingly suspended.
First, because never in my life, if I had seen magic performed, would I have had that reaction. No, if I had ever seen magic, I would have said, "Holy shit! Magic is real!" And maybe that's a reaction that means "Warning! You're going to grow up to be a speculative fiction writer!" but I really don't think so. I think our pop culture is so permeated with magic, and the possibility thereof (how many millions and millions of people have seen or read Harry Potter, or The Lord of the Rings, just to name two?) that the majority reaction - especially when the person having it is a teenager - isn't "that's not possible," but "magic is real."
I get why the writers would choose to put the line in there. It's like a big neon sign, telling the viewer to pay attention, emphasizing what the title cards in the trailer are emphasizing: this isn't myth or just your imagination. That big shiny explosion what you just saw is Real Actual Magic. But it's also lazy storytelling. If your story, which, you know, is called The Sorcerer's Apprentice, and you need big neon signs and title cards to tell the audience that the magic in it is real, well, you're doing it wrong.
And while I'd believe in magic, I don't believe in your story.