I don't agree with the GP either but your understanding of what it means to be a "psychopath" is even less correct. Psychopaths are highly impulsive and emotionally volatile. They would be far more likely to lash out in situations where they feel slighted than normal people would be.

There's this tendency (both among self-described high-functioning psychopaths and in the media) for people to think that psychopaths are highly rational and less emotional, but it's closer to the opposite - psychopaths are impulsively driven by the present emotions.

The main sense in which they are less emotional is that they react less emotionally than normal people to how other people feel and how they themselves would feel in the future. Because empathy generally acts as a check on your present impulses in most humans, this leads to more emotional, impulsive behavior, not less.