I highly doubt the 1k/50k stat - I have personally written 6 apps with more than that - so i've written slightly more than 1/2 of 1% of all apps in the app store with more than 50k users? unlikely...
They seem to be talking about active users, that use the app regularly while you seem to be talking about downloads.
Note in particular the quote just following the paragraph you are referring to: "For the typical app, less than half the people who download it use it more than once, said Guy Rosen, the chief executive of Onavo."
