If I remember correctly, at first Pokemon Go used Google Maps to display the actual map, but it still used OSM data for the spawning algorithm. Later on they made the switch to only use OSM.

The changes to Google maps api pricing made it entirely unsuitable for a whole lot of apps.

I do recall when that happened all of the complaints, madness from Google, but that's entirely their MO I suppose.

Interesting, thanks for clarifying!