According to the article, over a third of all users are "mobile net users," ie using the internet through their mobile phones.
...if current trends continue exactly as they have been doing in the recent past.
This is an important qualification. Any number of roadblocks could fall in China's path between now and 2020.
The people who draw a line between two dots and then make it go all the way into the future (ie projecting current trends forwards) are the same people that brought us the magic of house prices that never go down, a sharemarket where everyone was a winner, and the non-existent population explosion.
Clearly China is developing rapidly and becoming more powerful, but the future is not set in stone. Neither is China's destiny (nor America's decline).