Hacker and Programmer are categorically different.

There is significant overlap between the two groups.

Plumber is a category as well. The difference is that plumbers do not gather once a year to declare the Eternal Principles of Pipe. There is no Council of the Wrench. No one is arguing about the True Spirit of the Elbow Joint. They simply tighten the fitting and go home.

they didn't used to be and the difference was only barely developing at the time this was written