The problem here is that this thing doesn’t give a static image - when you zoom in, parts of it move around - and also extrapolate when farther away from the screen, i.e. somewhat 3D.
From that it’s obvious that it’s not just an image, but rather a lot of lines that compose the drawing - which the script just captures an image of at that resolution and spits out in a download box.
As a result, of that, you can’t just screenshot it by parts and stitch them, as the stitching will have obvious seams.
Also, your image is 2191x2191 in size, and a random image I gave it ended up in a 947x947 render. So, I guess, there is some randomness or other math involved.
I don’t know if I can help any more past that, but here are my 2 cents.