Link in the article seems broken to me. EDIT: FIXED!
The effect is ghostly yet technical, resembling something human-drawn but not enough to be confused as such.
Although it may be confused with a drawing on paper that was later very well creased and then dampened.
I put in an image of a straight line and got this:
just look at it
What does the backside look like?
My nephew everyone! Just look at them chubby cheeks!
This is giving me flashbacks of the string-art projects I did as a kid in the 1970s.
You have to wait a while, but upping the line count to 20,000 (unsurprisingly) leads to better results in the failure cases.
(compare to https://www.flickr.com/photos/jonthegm/5963582091)