The author isn't dismissing "window shopping". They're just dismissing the need to keep track of the "window shopping" in the history, since you're not changing anything in the history.

If you have state1, edit it and get state2, edit that and get state3, then go back to state2 and copy something and then go forward again to state3 to paste that something, why should the history from state3 (in reverse chronological order) then be [state2,state3,state2,state1] when it could just be [state2,state1]? This is what the author claims, and it makes sense to be. If I undo, don't make any changes, then redo, I don't want that undo-redo to then be part of the undo history.