Looks like a rough estimate to me.
Imagine the traction it would require at the start to do a 9 second 1/4 mile. Only on a dragstrip and with the right tyes. And even then - "maybe".
I don't really like Koenigsegg that much. Simply because they are not providing their cars to journalists for testing. Not as much as others.
It is their marketing model - they are happy with the high expectations and respect that ppl have towards Koenigsegg cars, and they know that magazine tests would, more than likely, bring disappointment, rather than exceed those high expectations.