I might be missing something but the first Facebook example used in the article seems wrongly applied to this problem. They just transferred the menu bar to the bottom. All the icons, which were at the top, are now just located at the bottom. They are now easier to see - the text doesn't hurt also, and probably easier to use (no conflict with the phones top-bar), which could be the explanation for the observed results. The only difference I can see is the switch of the hamburger at the top with a search icon.

Nobody ever asked me - for obvious reasons, because I might be blind - but I'm partial to an icon where you have a + sign ("additional" items) on top a V ("directional clue"; could be pointed in other directions for a pull-up menu for example) to form some sort of arrow.