Hand Tools Archive
He used a mill bastard file from the look of it. And he put a turn of tape on the end so one can bear down on the end and not gouge the wood. An MB file is slow in wood, so don't over do the projections, and half mm is all you need.
If you look at his details there are often very sensitive radii on edges, barely broken, but polished. These were also filed to blend with the plane work. Today, and back then with auto paper, you could sand these contours to the finish required but it would take even longer than files.