I didn't know that. Looking further, though, it's not quite as impressive.
Here's how it actually worked.
http://articles.latimes.com/2011/nov/27/entertainment/la-ca-working-hollywood-20111127
TL,DNR: It's not CGI, but they cheated. The gear work inside the doll is
just for show, and does not contribute to the drawing. The pen and arm are
actually pulled across the paper by magnets underneath the drawing board, moved
around by X/Y stepper motors, like a conventional pen plotter.
The Pierre Jaquet-Droz automata (he actually made 3; a musician, an artist, and
the writer) OTOH, were fully mechanical, and operated by cams and gears inside
the bodies.
...and 240 years before the Hugo movie was made.
pt