The linked article talks about the enormous upswings at the end of January, and pewdiepie was likely the funnel that caused that.

However YouTubers had picked up Flappy Bird much earlier, again for the "so impossible" angle (in the same way that there were tonnes of reaction videos to the game Amnesia, though it was far less accessible so had a lower ceiling). For instance-

http://www.youtube.com/watch?v=FMQSLT7e9Q8

The linked article assumes bots during this period, but more likely it was simply that it started making the organic transit through the YouTubers.