They were making an argument against my suggestion. You are right, they say that they know that their religion is superior because it is kinder.
By this reasoning however, Jainism is the one true religion. Their highest belief is: "Do not injure, abuse, oppress, enslave, insult, torment, torture, or kill any creature or living being."
More specifically, I think it was argued that the superior moral behavior of Christians is a demonstration of the truth of the religion.