Those are the public beta graduation statistics. They're not for private betas, they're for what it used to(!) take to go from public beta to a full-fledged site with its own design & logo.
They're also significantly outdated and not really relevant to site success anymore. A year and a half ago Stack Exchange changed its policies on site graduation. The short version is they were previously set up with the presumption sites needed to be high-traffic to be successful, but they recognised over time that small, low-traffic sites could also be very successful, and so there's no pressure to have that visitor count. You can read more about that here: Graduation, site closure, and a clearer outlook on the health of SE sites
Also as Zizouz212 says, this is a private beta. The majority of any site's traffic comes from Google. Google can't reach us yet (try opening this page in private browsing), so our traffic's going to increase by an order of magnitude once we go public.