For better or worse, that is the inherent assumption - that a smartwatch is a companion device to a smartphone. The idea of ditching the phone entirely is, arguably, an unintended consequence of releasing smartwatch variants with built-in LTE connectivity. Giving the app developers the benefit of doubt, it's understandable they don't want to make a standalone app for a fraction off the smartwatch models, where they can do with one simpler extension app for all smartwatches.
