He sounded like he was asking for his headphones back. He asked a few times. Did they steal his headphones? Is that why he was following them, to get his headphones back? If someone stole my headphones I would follow them also.
They follow the Asap Rocky guys, security tells them to get lost. The one guy flails the security guy with the headphones breaking them, things claim down a little and the rappers decide to just leave. But the one kid won't leave, and decides he needs to get paid for the headphones he broke messing with the security guy.
I'm not sure how it all started, but most reports just say the rap crew was just wandering around with fans when they came across the Afghans.
Edit, see the headphone fight here between 32 - 45 seconds in -
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