The full sentence was: “ The problem is that s-pedelecs are technically lumped in with the scooters, even though there is no throttle and there is absolutely no way you are going to sustain 40 Kph+ for anything but a very short period.”
He is explicitly talking about S-Pedelecs which are the fastest legal E-Bikes in most of Europe. He never said that you are generally not able to sustain 40+ MPH in general.