It’s a scam.
I almost fell for it but the guy was a little too persistent and something in my gut told me he was a scammer. I called the little a$$hole a scammer and he got all irate on me. I told him I was reporting him…and I am! You should do the same!
This is what I did to get rid of his annoying pop up: force quit Safari, turn off wifi/internet, hold shift key while starting Safari again.