Was wondering the same since, this is about top speed and not about acceleration the weight shouldn't matter much at all, since it has no direct influence on the air resistance.
Would be interested in knowing, if a human powered vehicle on steel rails with steel wheels with the same air resistance could be faster than this just due to the lower rolling resistance.
Weight shouldn't have as much of an impact on acceleration because as muscle mass & power goes up, weight goes up as well.
But more weight inside the shell doesn't increase air resistance, while it does increase power. So a heavier rider with greater sustained power output will, in an environment where wheel friction is trivial, go to a considerably faster top speed on flat ground.
Did anything happen to F = m × a in the last 20 years?
Acceleration a is heavily dependent on the mass m.
Since a = F / m having half the mass would result in double the acceleration with same amount of force F available.
If they're putting athletes into this thing, the bigger the athlete, the more force (okay, the more power) is available for propulsion. They have bigger muscles which store more glycogen and have greater total mitochondrial activity, because there are simply more of these cells available to do the work.
Unlike in high school physics, we have to account for drag, which is a lot more important than mass at these speeds. F=ma is true, of course, but you have to think more about what F really is.
Would be interested in knowing, if a human powered vehicle on steel rails with steel wheels with the same air resistance could be faster than this just due to the lower rolling resistance.