I think he's referring to the occasions when you have the shot all set up, club chosen, direction and power figured out and then for some reason find yourself with a different club to the one you wanted. It's happened to me a few times but I've only once not noticed before taking the shot.
I think what usually happens is you knock the scroll wheel on your mouse which scrolls through the clubs in your bag. Easily done but it's also easy to double check before you start your back swing.
Changing scales isn't something I've encountered more than a couple of times. There are situations on the green where the putter returns to the scale you were originally given. I might be wrong but I think if you change to a pitch or chip shot to check the break from that view it may happen when you go back to the putter. As I say though, this may be wrong. I'm sure there is one scenario where this happens though, just not sure what it is.
The moral is to always check which club you have in your hand or which putter scale you're using before you start to swing. And be sure the distance and club tally. I've sometimes had it show a 4 iron but a max distance of 135 or something. When this happens I always go back to club selection, change to any club, then back to the one I want.