Xardas is actually so funny for handing you an invaluable ancient tome that he checked out of the monastery library 20+ years ago and never returned when you tell him that Pyrokar requires proof that Xardas can be trusted.
Xardas knows that Pyrokar is never going trust him again and that nothing he can say or do is ever going to change that. He also knows that the ritual at the Circle of the Sun cannot be completed without Pyrokar. So, instead of even trying to win back Pyrokar's trust, Xardas does the exact opposite and gives you something that is 100 % guaranteed to piss Pyrokar off even worse.
And it works.
When you bring the tome to Pyrokar, he specifically tells you that, yes, he's finally agreeing to meet at the Circle of the Sun, but only so he can tell Xardas exactly what a bastard he is.
