Reasonable question.
Before I get into specifics, let's address the general concept of how to grab in a non-garbage way. The most important element is that your grab must accomplish something. If you can use your grab to break your opponent's balance and structure, or set up a strike, or set up a more controlling grip, or apply a throw or joint lock, then it can be counted as potentially effective even if not all the technical details are perfect.
In the video the instructor demos counters for two types of grabs.
The first is a fully extended cross-body wrist grab from underneath against a raised hand. This particular grab is useless for setting up any kind of lock, throw, strike, or improved control position. The cross-body arm extension compromises the attacker's structure and sets him up for some easy counters. It's also not a common untrained behavior, so there isn't even the excuse of learning how to deal with a typical street attacker.
The second "attack" is apparently meant to simulate a double-leg takedown, but it's missing everything which makes a double-leg effective. The attacker is coming in with no setup, from too far away, with his arms outstretched long before he could reach the legs, compromising his own structure by leaning his head way to the side, attacking the wrong side, feet pointing the wrong direction ... it's just a mess. Any competent fighter of any style would easily stop the entry before the attacker completed the grab. An untrained football style tackle would actually be an improvement because at least the attacker would have better alignment for generating speed and power.