The key part of that sentence is "in the 1930s".

Civil engineering has become massively mechanised, so the vast majority of jobs in the industry are highly skilled. A job that would have needed 200 men back in the '30s is now done by three men and a giant machine.

Make-work is make-work, however you slice it. We could choose to build bridges and roads like they did in the '30s and create millions of jobs. We could also impose vast tariffs on imported cloth and ban automatic looms, creating millions of jobs in the textile industry. Philosophically, it's no different to paying people to dig holes.