There is a common misconception here. There is no such thing as non-lethal force anymore. It is now referred to as lesser-lethal force.
As for understanding how this works, you'll want to learn about a Law Enforcement agency's "use of force policy", which describes the escalation of force in a specific situation. The escalation of force, in its basic description, states that one should use their own common sense and judgement to use the least amount of force necessary to stop the threat.
For example, you would not pull pepper spray out on a man with a gun, but you may use a pepper spray on an unarmed man who is aggressively fighting you, trying to cause injury.
Likewise, you would not pull a gun on an unarmed man, but you might pull a gun on a man with a knife who is brandishing it.
Clearly this video is a very good example of someone not understanding how to escalate force properly, and thus should not have been given the option to respond to these situations accordingly. This is why officers involved in shootings are heavily scrutinized for their actions, and must justify their reasoning for taking the actions they did.