Paraphrased:
The narcissist’s smirk is a subtle but telling expression that occurs when a narcissist experiences pleasure from manipulating or deceiving someone.
For narcissists, the smirk usually reflects contempt, which is a deep-seated disdain or lack of respect towards others. For narcissists contempt is tied to their belief in their own superiority. They view others who do not serve their needs as worthless or beneath them, showing a complete disregard for how their actions impact those around them.
You are very lucky not to have experienced this firsthand. I’m not so lucky, and I can tell you it is real. They get off on deception and power over others, but that’s also their weakness - it’s a compulsion. While they imagine themselves to be masters of manipulation and control, the urge to gaslight and fuck with people is so great that they typically change jobs, locations and social groups pretty often, depending on how sophisticated (or lucky) they are. They get caught because they can’t help themselves. If they see an opportunity to manipulate someone, they will take it - they overestimate their ability to fool people.