Interesting story here.
In heroic societies (Helenic Greece, Viking, and to some degree Roman, etc.) the ruling class, the elite, the masters would often call themselves the Truthful Ones.
Why? Because the masters did not pretend to be something they were not. The slave class were considered deceptive, untrustworthy because they would sneakily hide their malevolent intentions behind a guise of "niceness"
Meanwhile the masters were proud and joyful and dominant and if they expressed affection - it's because they were feeling affection and genuine warmth. They expressed affection in the knowledge that if they wanted to they could also break that person.
Slaves do what they think other people want them to. For that reason their word can't be taken. In the Roman justice system, evidence from a slave on a legal matter could not be accepted unless it was extracted via torture because they thought otherwise they would just say what people wanted them to, rather than the truth.
Illustration of what I'm talking about. I'm not into the torture thing so much, but they have a point.