Sure you do. Call the police. Record it, capture the details for evidence.
> Just stand back and watch?
Again, you're welcome to call the police. But no, you don't just get to rush in and start interfering because your sophisticated understanding of the circumstances as a complete nobody make you feel like Captain America.
> That's the world you want to live in, one where kidnappings are normal?
It's obviously not a "kidnapping". Nobody seriously believes that -- most obviously, Brad Lander, who wouldn't be screaming for a warrant from "kidnappers".