Google's is initialized with a gridded dataset, ERA5, from ECMWF. Using ERA5 is the current standard here, and ECMWF themselves build on that mostly now. Meanwhile, Aardvark tries to do the same directly from observations.
"Observations" is overloaded; it's really any "raw" weather data product, like satellite imagery, surface station measurements, or weather balloon traces. I'm handwaving away a lot of complexity here.
The AardvarkWeather model is a significant new development and paradigm shift - it's one of the first models of a new class which do not require an analysis, and can directly use the "raw" weather data observations that are typically used to perform data assimilation.