It is a dedicated Google Pixel stand. The XS Max probably works more out of coincidence, as it is similar in size with the Pixel and is having the coils placed similarly (however, I'm not sure it charges with optimum efficiency).I've never once thought about where I place my iPhone XS Max or my Google Pixel 3XL on the Google Pixel stand. It just works.
The Airpower mat otoh is intended to charge a multitude of different devices with differently placed wireless charging coils, such as e.g. Watch, iPhone 8, 8+, X(s), XR, XS max, AirPod case, future devices ... at any given position on the mat (and it has to be a mat as there's probably no sane way to provide a stand functionality for all of the mentioned devices).
When you just charge one or two similar devices, a dedicated stand is fine. When the charger has to be agnostic of the form factor of the device to be charged, it's a different engineering challenge altogether.