Great interview. At the start Dave kind of conflates 5G with millimeter wave 5G.

The big difference between LTE networks and 5G networks is not the frequency ranges used, low band 5G is perfectly feasible. The big difference is the linear increase in information capacity per antenna in MIMO (multiple in multiple out, many send many receive antenna) verses the logarithmic increase per antenna with single antenna to single antenna links. (while power his held constant)

If you want to learn more this is a great intro to channel capacity with MIMO, http://complextoreal.com/wp-content/uploads/2013/01/mimo.pdf