True, but if I recall correctly spatial multiplexing can be used to increase channel capacity.

Using the same 50db SNR for WiFi at 40Mhz we get:

  ((40000000)*(log(1+100000)/log(2)))
  ans =  6.6439e+08

or 664Mbit/s, however, 802.11ac can achieve higher than that by using MIMO. I unfortunately don't know the formula for max channel capacity for multiple streams.

It doesn't seem like they are using this though in their experiment.