Because all new accounts have to be approved before that user can post with it. They're approved every few hours, about 2-3 times per day and his was just approved. It's only been a few hours, because even I sleep.
As for why all new accounts get approved and just aren't automatic, remember when we were constantly besieged by bots signing up and smashing us with ads for Ugg boots, "free" laptops and porn sites? Well, it's been forever since we've had that happen. In the end, there's no mysterious conspiracy, hundreds of accounts were deleted as part of every attempt to clean the board. All of them had been unused for a minimum of a few months, with several being years old, some never used and quite a few users having multiple accounts deleted.