The accessibility guidelines we have, e.g. WCAG, usually say that tab is used to tab through separate interface elements. When you're still inside an element - for example if you have triggered a dropdown list in a text input field - you use the arrow keys to navigate within and enter/space to select elements.
Say tab was used for all (intra and inter) navigation tasks. In that case you risk suddenly having a thousand item list that keyboard users will then have to tab through to get to the next interface element. That is not good UI design.
Anyway, we can disagree about proper tab behavior here. My intention is to support the article by highlighting sloppy behavior from Maps.app. A case in point, the arrow keys don't work either.
To see, type a few characters in "Search Maps" until suggestions appear, press down arrow key, ... no suggestion is select, instead the search box looses focus and the map moves?! While messing around with this... I noticed that pressing the right arrow before pressing down arrow (sometimes??) begins selecting suggestions. Seriously, go mess around with it... but it's super finicky.
This is the state of Apple UI polish and consistency today.