An honest question: how can you be so sure?
(Also, a pet peeve- your rights and responsibilities page. I didn’t get the memo that not believing in a god signed me up for a whole new other club. It’s a personal choice, belief, whatever; it’s not a church without a centre and it hasn’t got a specific creed. Grr.)
An honest answer: About what?
Not believing in God doesn’t “sign you up for a whole new other club.” But there are certain rights and responsibilities people have even without religion. So, in that sense, these rights and responsibilities are atheistic.
(Besides, that page is a satirical jab at intolerant theists — it’s not intended as a set of rules embedded in atheism.)