What are the damning parts specifically?

The color saturation is a little different, but the camera is at a slightly different angle to the sun too.

The black square is a bit suspicious.

I was looking at that video too and thinking it doesn't look or feel natural. It's a good trick and actually a good demo. I think the physics are kind of off in the final video though.

What's off about your screenshots? It looks pretty consistent to me, e.g. the shadows and the marking of the wings.

I definitely noticed that they didn't show the landing clearly. I expected him to fall if he had any kind of velocity going but it wasn't clear, and that seemed fishy.

1) Missing square element in real footage. 2) What bothers me more is that shadow properties are not consistent. In CGI it is more diffuse and changes properties like if the Sun is positioned 10m above.

It could be the camera being wonky, legitimate post-production work, auto gain adjustment, etc.

So, no, look at the equipment used, look at the mechanisms involved, and tell me that it is completely infeasible. Don't rely on analysis of some cheap Youtube video.

As for the black square, I'm willing to chalk that up to being under the fabric until its stretch taught.

EDIT: Black square is not under the wing--probably a patch if its real.