Did you read the first footnote I wrote in the piece? It’s actually about this exact thing you are talking about:

In many graphical interfaces that expect a mouse as input, the programmers will make the clickable area of the upper row buttons the same as the lower row ones, although this will be invisible at first. You can hover with your mouse over the buttons and then, magically, a button shape will appear. It’s not going to be a nice 3D-button shape however but just an outline. This serves no functional purpose. For instead of showing the user where all the buttons are from the outset, the whole affair becomes sort of a hide and seek game, where users have to guess which item they might be able to click.