I can give you a technical explaination, but it'll need a lot of words cause I'm not good at explaining!
I'll try to keep it short and simple: The kind of transmission it probably had was a CVT (Continusly Variable Transmission) and as the name implies; that transmission automatically changes it's gear ratio as per throttle position and the wheel's spinning RPMs (Revolutions per Minute)...
So, this bike can 'virtually' achieve speeds in excess of 100km/hr cause there are infinite gear ratios!
Imagine a motorcycle's engine is spinning at 8,000rpm and the transmission is in first gear which has a 3.35 : 1 gear ratio, does it mean that the rear wheel is spinning at 8,000rpm too? No, it's not! Because: 8,000 / 3.35 = 2388 RPMs!
This means, the wheel is spinning at MUCH less RPMs but with more torque or twisting force! Hence, we start our cars and bikes in first gear and not in sixth to get up to speed quickly!
Now, keep the RPMs at 8,000 but lets put that transmission into into 6th gear which has a 0.9:1 Gear Ratio. Lets do the math: 8,000 / 0.9 = 8,888! Hence, wheels are spinning FASTER than the engine!
And we all know, faster wheel spin = more speed!
Hope you understand.