"Physicists are to academic philosophy what retired engineers are to physics"?

I apologize if this is the wrong subreddit for this kind of question. I've encountered this claim (or variations of it) here and there, and I'd like to know if you could give me some context. I assume it's an in-joke meme, but what is the implied relationship between retired engineers and physics? I've mostly seen it repeated by philosophers of science and commentators on discussions about free-will compatibilism.