I also fail to find a cat on this picture.

That's because Histogram of Oriented Gradients is not invariant to object orientation: http://en.wikipedia.org/wiki/Histogram_of_oriented_gradients... (second paragraph).

This example app was trained on upright cats.

Nope, still fails on a cat-upright version: http://i48.tinypic.com/2i0ejxl.jpg

That's not a cat, that's a dinosaur.