His connection with one of Silicon Valley's premier venture capital firms (Facebook, Skype, Twitter, etc.) gives him access to data that's not always publicly available. Like iOS and OS X device share data as seen by Baidu, China's leading search engine.
Happily for the rest of us, he shares it.
FOLLOW-UP: Evans says these numbers are available on Baidu's developer site, although I couldn't find them. "I never post anything that isn't public!" he says.