All the report says is that the error wasn't noticed at take-off because of the length of Perth's runway and "the design of the aircraft".
It looks as if the correct take-off weight was 55 tonnes, whereas the estimate was 9 tonnes less: 16% too low.
That would have carried through into the calculation of the take-off velocity, but perhaps the pilot, with plenty of runway ahead, delayed rotation. Or the pilot might have sensed that the aircraft felt 'sluggish' and increased the thrust. Whatever, it was a potentially dangerous situation (What if the stickshaker activated just after the aircraft was airborn?)
There's another thread that refers to an incident where the thrust settings were too low. Both the weight issue and the thrust issue could be addressed by 'Force = Mass x Acceleration'. This already happens by intuition, but perhaps the takeoff procedure could incorporate an airspeed check at, for example, 5 seconds after the thrust is applied. A 16% weight error (or a 16% thrust error) will result in a 16% reduction from the anticipated airspeed, prompting a manual increase in thrust to take off and a check of the weight estimate while in the air.