Aside from that this article only comes to the conclusion of broad implications and the author himself says he used both interchangeably in his book, this is an American source and the headline for this post is British. I don't know about American Engkish, but there is no expectation of a stone being worked by humans in British English. In common usage here a rock is generally bigger than a stone - I'd say whether you can throw it one-handed is roughly where the extremely fuzzy line is - but you could absolutely just pick up any small piece of stone from the ground in nature and call it "a stone" without anyone questioning it

https://www.merriam-webster.com/dictionary/stone

As long as I'm here, should mention that I didn't even realize I was replying to you in the comments of that one about the sandpaper. At the time, I'd intended to toss in that parenthetical with no context and wander off and, upon noticing the coincidence, debated editing it out since it could look like I was following you around. No malice in it and while we may cleave along the rock/stone question, I respect your efforts.