Deefer, there's also the old adage that if the real world you can see out of your window doesn't match what your computer says, reality is almost certainly correct. (That applies to your car's satnav too.)
On the one hand, you might think someone would have looked out at the runway and said, wow, isn't that a bit short for a max weight takeoff? On the other hand, it was dark or at least dusk, so the shortness of the available runway may not have been so obvious?