The top speed means exactly that - because the Smart Wheel is a pedal assist this means it helps you accelerate until you reach 20 mph and no further. You're correct in stating that the top speed is also set in accordance to the US Law (or European Law, which allows for speeds up to 25 km/h).
We're sorry about the confusion about "the first line of electric bicycles" - this was of course meant to inform the reader about the first line of e-bikes that we're introduced by FlyKly, not the first e-bikes EVER.