Arguably, time spent reading HN is a legitimate part of becoming/remaining a good developer. Certainly, spending time socializing with coworkers is a required part of work, many places. Spending some amount of time unwinding at the office is arguably required for mental health and therefore a functional component of remaining a worker -- does that count as working?

"Working" is an ambiguous category, it seems to me. One definition of work (call it "productivist") says that we're only working when we're literally producing something valuable. A more organizational view might hold that "work" is whatever you're socially (often implicitly) required to do to keep your job (whether measurably productive or not). And a third more holistic definition would include stuff like exercise or professional development that are not always directly "required" by anyone, but that you might go crazy without doing...