Squares are rectangles. However, you will note that they changed the button format which suggests that they are they where treading a little close to Apple's design / long standing trend of having a single button. I still hate the fact that they use a single physical button to simulate more than one button based on how long you hold it down so IMO it's not really a benefit just an aesthetic choice.

Apple does the same sort of thing, but even more so. Tapping, holding, double tapping, triple tapping, tap and hold, etc. The home button is ridiculously overused, a consequence of less hardware holding more and more uses.