I don't think compete.com is all that accurate either. I saw some numbers on twitter.com and it reports around 30k uniques per month -- a little low for a site that gets a few million tweets a day. By comparison, quantcast.com reports twitter getting around 31 million uniques per month -- much more plausible.
You probably mistook thousand for millions, I can't imagine Compete.com failing at such a high profile site without them noticing and fixing it.