Yeah, Barre granite is tough, but saying it's too hard for a grinder isn't totally right. The key is keeping it cool, which you did with the water bottle. A cheap diamond blade on a grinder can work for small jobs if you go slow and let the tool do the work. It's not the right choice for big slabs, but for a quick corner cut, it's a solid fix. You weren't just lucky, you used the right method for a small task.

Your cousin might have set his hopes too high, iris483. Those "lost civilization" books are almost always packed with wild guesses instead of real facts. The bad pictures are a dead giveaway you are getting a low effort product. It is annoying but not worth getting actually mad over.