No, this is not diffraction.
Let's start by recalling how the image is formed by the lens (focused and defocused):
Each point of your large aperture lens contributes to just one point of the defocused image:
(by the way, this also shows why aperture size affects (de)focus)
And what happens if you place an obstacle (your hands) near the lens?
Not all defocused rays can reach our image, as a result the image appears more focused and slightly shifted.
And this is what happens in your photo - by covering the aperture, parts of the background become shifted and warped, depending on the obstacle shape.
...and now I found the same effect on physics.SE, having much better explanation and pictures!
https://physics.stackexchange.com/questions/111006/how-does-light-bend-around-my-finger-tip
