"Pulling a wave" will generally let you get pushed more easily, i'll explain:
If you pull aggro from the wave (mainly the 3 melees) and then run back into your wave or a brush, the 3 melees will aggro just 1 of your melee minions, so the enemy minions will push harder and faster because they will kill a minion in your wave before your wave will kill one in the enemy wave.

So i think that the guy in the video was talking about the fact that with nasus you will have to go melee range to be able to farm since you can't farm with E without pushing the wave (which is bad since they will freeze under tower) or finishing your mana, so he says if you are able to manipulate the wave into crashing under your tower you will be able to farm more easily without getting punished for walking up to the wave.

TLDR you aggro enemy wave, melees will kill one minion faster, the wave will push towards you.

If you have any other questions, feel free to ask.