its just a pop up from the browser your all good, just a typical phishing scam. and also you didnt have to unplug it they make the scam pop up in full screen so you can see anything else so just press ESC to exit full screen.
Basically if he didn't download any programs or apps hes in the clear.
i do recommend installing this extension down below so it would block and show CLEAR warnings about websites like this since the older folks do know much about computers:
the link
(malwarebytes)
