They are basing an average “pay per click” “pay per advertisement” number that may not be entirely accurate in every case. Also as I said, as far as pay per click, from what I understand its not much compared to what you get from running advertisements, but as i said, advertisements AFAIK do not pay out everytime someone clicks on your video and doesnt let the advert play through.
Like I said, no doubt in my mind they make a great chunk of money, but I don’t think that site is accurate at all, I would imagine actual earnings are on the lowerisde of their estimates, the fact that the range of earning it shows is so far apart from low to high should show you that they have no idea and it’s probably a bit inflated.