I have to ask because it's just going to bug me if I don't.... What exactly were they trying to convert you to? Unless there is some established set of atheist doctrines I'm unaware of, I can't think of what you'd be converting to. How would you even adopt a new belief that you now, by definition, lack?
That's pretty messed up. Heck, even if I believed that, I wouldn't go around telling people this. Maybe you were just dealing with a jerk with a chip on his shoulder, IDK but that isn't a belief that just naturally stems from atheism. That is an individual with a personal vendetta against religion.
And I've heard many theists express similar sentiments towards most anything they consider "secular." I try not to pay attention to those as I know they don't represent the entirety of Christian thought. There's people who believe the theory of evolution should be outlawed because it somehow leads to atheism. Crazies are abound in most all people groups.
They are the actions of individuals. Best not to judge whole swaths of humanity by the silly actions of a few of each group.
There is only one fundamental to atheism. Can you guess what that is?
Like I said... Some people are overly zealous in their beliefs, no matter what those beliefs may be. That some of these overzealous crazies don't believe in gods still doesn't really make atheism any more of a religion.