This makes no sense. The examples he gives of "double-clicks everywhere" are all instances of the same thing: items that are selected with single-click and open

This makes no sense. The examples he gives of "double-clicks everywhere" are all instances of the same thing: items that are selected with single-click and opened with double-click. We're not "trained to double-click anything", unless some particular trainer is extremely misguided. Double-clicking is used when there is some action available for an item in addition to the single-click action, where the double-click usually leads to both actions taking place: we single-click to select files and double-click to open them, single-click the title bar to activate the window and double-click to maximize, single-click the window menu to view the menu and double-click to close the window (which is one of the options in the menu). Some examples of things we only single-click: buttons, scrollbars, tabs, menus, dropdowns, text (for selection). Single-click is everywhere. Everything that can be double-clicked can also be single-clicked. Single-click is the default. If a single-click only leads to an item beings selected, that's a pretty good hint to try double-click if you also wanted it to be opened. (Incidentally, what do those who double-click everything do when they want to select a file? Do they just open it, close it again (leaving it selected) and accept that as normal?)