The main tactic is shoving defenders into the keeper as the ball is being kicked so they are indirectly fouled and temporarily stopped from making their way toward the incoming ball. No hands on them as the ball arrives so nothing is ever called. Those shoves on defenders as well as bear hugs/tackles on defenders during set pieces are not called the vast majority of the time now as it happens multiple times on every single set piece (even on the VAR goal Arsenal was bear hugging/impeding multiple West Ham players) so it is the equivalent of college basketball can't call them all defense but definitely illegal. It has gotten worse in recent years as teams realize the refs don't call it so they push things even more, but the comment was about how Arsenal has led the way in terms of the push things even more in recent seasons and especially this season.

Fouling a keeper may be more clear cut, but the amount of illegal play on set pieces that has not been called this season has been insane and something does need to happen to change that or it will continue to get worse and make the game unwatchable.