After reading the prequel, it really is cruel.
Sauro was debating about bursting in to save Arsenyo from the torture but knew he wouldn't manage to get him out, so at the stake was the only chance.
But that was when Arsenyo (after holding out from torture to avoid implicating Sauro) gave up, and accepted the salamander that offered to save the both of them, and burnt the executioners.
It is what made Sauro think that his friend had been killed a long time back and that he had been deceived by a demon, when all along it was just his friend whos only sin was wanting to not die a horrible death.