I agree there is a huge difference - but folks who choose to pursue a part-time job are literally not retired - they are working. Working is the opposite of retirement, lol. The past 3 years before I retired, I knew I probably could. Had someone really pissed me off at work, I probably would have. I reduced my hours. But I was not retired. I would categorize folks who quit their primary career and take on part-time work as 'moving towards retirement'.
It's not really an important point. I think it's interesting that many seem to 'retire' but still feel some desire to work (for whatever reason) because that is so far from my own personal mindset. I am done. I will never 'work' again. I admit that it is hard for me to relate to folks who want to continue to work in some capacity but again, whatever works for each of us is cool, we are all different people with unique situations.