What is the manufacture date on the inside of the driver's side door jamb? That's a fairly low # of miles to be rejected but I guess if it's something like a dead battery that they had to replace they might have given the person a new car.
In most states by the way this would not be legal... to sell a car that had been previously sold as new to another buyer as new... so if I were you I'd be digging a little further into this.
Another explanation is that Tesla was doing demos with this particular car and someone paired their phone to the car, could even be a Tesla employee.
So, it's more likely this car was used for a test drive or something than that it was a 'reject' that was sold to someone else and then re-sold to you.