Comment by convivialdingo

If you watch it very slowly, the paper initially folds under the mouth and then it blows out straight.

I'm guessing the initial puff creates a high pressure area on top of the paper, rolling it downward and back. Them after the puff has pushed the air away, there is now a low pressure zone on top of the paper which lifts it up as the air below is rushing upwards around the sides of the paper.