“over time” is key in the description of how this works. I went on a work trip with a colleague recently and it was only about 24 hours after we met up that my phone notified me there was an AirTag following me, because she had one on her car keys. You wouldn’t be notified straight away.
GSF is where most of Google's invasive user tracking happens. It's proprietary, closed source and is not part of AOSP (Android Open Source Project). It is, by definition, spyware.