Hello there. Remember Kent added the cube, then added a Subdiv level 2 to the cube and applied it, so he can have enough geometry to work with. Once you apply the SubD modifier, the resulting shape is not a perfect sphere, it is then that you do the To Sphere command or Shift + Alt + S.
Remember the change is subtle, so keep a close eye on the shape changing a bit. You can both drag your mouse or you can type “1” on your keyboard to get the full effect of the To Sphere command. Hope this helps.
