Stolen card for sure… I guess you could have taken his payment of 4k and called the CC company and had the Police there waiting for his friend. It sounds very risky to the scammer as they never want to have an associate show up and get busted then roll on the perpetrator. He may of asked you to WU the balance after you made the charge to avoid what I described above.
Did this guy have an accent and speak fluent
Drop a security freeze on the 3 Credit Monitoring agencies as these scammers are relentless.