That gave me pause, too. I think they mean it's not a replica because there's no original -- or rather, it is the original. That is, it's not a copy of any part

That gave me pause, too. I think they mean it's not a replica because there's no original -- or rather, it is the original. That is, it's not a copy of any particular Viking-era ship found buried in mud or whatever; it's an entirely new ship, made using documented (and inferred) methods from the era. It's as if someone made a ship that was quite like, yet also distinctly different from, HMS Victory (or the Santa Maria, or whatever historical vessel floats your, er, boat): not a replica, more a sister-ship.