I kind of see his point, actually. Take another event that is good, but not national caliber for high schoolers: the 800- 1:55, 1600- 4:10, the 3200- 9:20
Professionals can run under those times for around 3 times the distance. So, why can't a professional run under 50s for twice the distance?
Obviously, it's because of the physiological requirements of the events and the differences in the requirements for the 400, which is much more anaerobic, and the 800, which is more aerobic (believe it or not).
I think the reason we see pros going 3 times the distance at the same pace the high schoolers can do in the 1600 or 3200 is because those events are almost entirely aerobic and most high schoolers simply aren't developed yet.