It is in fact accurate for him to have made the shadow smaller as it went up the wall like that. Shadows get longer across a plain that is perpendicular to their position but when they hit a plain that is parallel like that it is relative to perspective.
I will add that in addition to blurring as he did the opacity should vary as well meaning the shadow should be both sharper and darker the closer it gets to the casting object. I also think that blurring the way he did is not a realistic way to do it because the shadow would get more diffused the farther away it gets. One blur added to a portion of the shadow does not achieve the effect that nature creates.