I not only believe these numbers, I believe that greens are generally much slower on the stimpmeter today that most golfers believe. I seriously doubt that most golfers have a frame of reference for extreme speeds, nor an ability to accurately assess what the speed of most greens is. Why would we? I think we understand green speeds in the same way we understand off the rack clothing sizes; greens come in S, A, F, and VF. What we consider to be VF might be in the 10 range, probably a bit less.
I recently played a round at a course where the greens were actually running at 12, by order of the owner of the club, who has the money to make his wishes come true. I had NEVER been on anything like that, and it changed putting 100%. Really no way to describe it.
Two days later I was back at my club for my regular Saturday round and all my buddies were commenting on how fast our greens were at that moment. Based on the average distance by which I left putts short, I'd estimate that our greens were a 9 at most, and more likely 7 or 8.