I do see, mostly from Americans, self introductions of the form "I'm so and so... and I love Jesus" in contexts that have nothing to do with religion. I've never had anyone bring up their atheism or agnosticism in that way in a non-religious context.
Have you ever encountered the atheist version IRL? Not just in internet bickering?
Maybe it was regional - I wouldn't know which region they were from off the cuff.
My family is mostly C of E and I don't recall any of them ever bringing up religious topics with third parties unprompted, so it did strike me as pretty weird.