Possibly effective doodling in the design space of systems? I personally hacked at untold number of experiments with different approaches, and was doodling like mad over at least a decade. I have bookshelves full of notebooks covered with object graphs, system sketches, etc. It's not just coding.

DBA or sysadmin, I would imagine. So more “never wrote application code” than “never wrote a single line of code for anything ever.”