That figure is extrapolated based on the longest photon path length through the device. It isn't based on real experimental results (the device was demonstrate

That figure is extrapolated based on the longest photon path length through the device. It isn't based on real experimental results (the device was demonstrated with n = 4), and it does not take into account the exponential quantity of photons you'd need to pump through the device before getting a measurable result. Fundamentally, there's nothing this device is doing that a classical computer couldn't, so there's no reason the exponential base should be any different under physically realizable conditions.