The guy confessed to being an atheist. Now can I say anything from the religion's point of view to prove to him that he is wrong? Nope. Judging by the way he behaves with you and others here, I don't wish to be debating with him further more. Not my cuppa. He is free to believe what he wants.
And my saying peace is just my personal way of saying "adios" and "I'm outta here" nothing more. And no not all Muslims, will do the same. Just my own style, and hope you understand.