A farm with 2,500 dairy cows produces the same amount of waste as a city of 411,000 people.
Searching the document shows that the actual numbers put forth by EPA are
Animal farms produce as much manure as small and medium-size cities. A farm with 2500 dairy cattle is similar in waste load to a city of 411,000 people.
The quote on cowspiracy.com takes this entirely out of context and talks about generic waste instead of specifically about manure. Additionally this difference is not surprising as even a Turkey produces 13x as much manure per year as a human. What biological difference causes this huge difference I do not however know.
2500 dairy cattle, with an average size of about 1200 lbs, produce roughly 75,000 lbs of manure each day.
411000 people, with an average size of about 178 lbs, produce roughly 381,031.25 per day.
Thus a single dairy farm of 2500 cattle is severely lacking, if we consider only manure, compared to a city of 411,000 people. You need 4 more farms to get close.
With average human weight of 177 lbs, and roughly an ounce of poo generated per 12 pounds of body weight, per day. http://greatist.com/health/poop-health-embarrassing-questions
we may calculate (177.913/12)/16 ~= 0.9kg/day output @ 1 oz per pound
Clearly, cattle produce more dung per pound of body weight and per capita. Humans have a body-to-stool ratio of about 192:1 while cattle seem to be about 40:1.
This means, with ~1.4 billion cattle on the planet, we are close to tied for total crap per populace. There's about 5 times more of us, but their poop is about 5 times larger per body mass. Get your head ..or butt.. in the game people!
Note: there is a fair discrepancy between sources on how much an average human poops. It seems to vary between 1-2 pounds per day roughly. Conclusion estimates using the lower amount, if we double then it's even more accurate.