A person's self-confidence is hardly ever unfounded, there must be some degree of accomplishment behind it.
Uncle San has seen big scenes, it's unlikely he'd delude himself for no reason to believe he could hand four-to-one odds.
And so, Ji Changsheng begins to suspect Uncle San has attempted such a feat with the Four Immortal-Slaying Sacred Swords in history, perhaps even victorious over two Ancestral Witches, or two Supreme Unities.
This led Uncle San to conceive the notion that with the Slaying Immortal Sword Array--a two versus one matchup is no big deal and he can easily handle four at once!
When Uncle San ascended to saint-hood, the original four Supreme Unities morphed into four Saints.
The moment this notion crossed Ji Changsheng's mind, he heard Uncle San on the other end say: "The teacher didn't lie to me, he said the Slaying Immortal Sword Array could be one against four. At first, I thought he was boasting, but it turns out it's true! How generous is the teacher?"
