Hearing Alister's request, Zanna immediately agreed, "Sure! Not to brag, but I am very proficient in magic. At least, I am not confident that I can teach you aura arts but in magic, only Fantasia can defeat me!"
When Alister heard Zanna's immediate reply, he sighed in relief, "No need to teach me aura arts. I am not confident in magic but my swordsmanship has reached the realm of killing a god."
After hearing Alister's "brag" about having a swordsmanship that could kill a god, Zanna couldn't feel that Alister was lying to her which could only mean three things.
One, Alister was really good at concealing his lies that even a demigod-level existence such as herself couldn't detect.
Two, Alister was telling the truth from his perspective. Alister believed that his swordsmanship could kill a god so from his perspective, his belief was the truth even if it wasn't a fact.